Is very likely the whole idea behind 'post formats' was inspired by Tumblr. That don't mean that Tumblr is an end on itself (they don't support titles for every post type, for one), yet still is a good reference.
Generic fields used in all Tumblr post formats:
—Site to post (a WPMU plugin territory)
—Date of publish (already on core)
—Content source (by now is only on 'Quote' post format, yet it may be good to use in all formats)
—Tags (already on core)
—Custom slug (already on core)
—Send to twitter (another plugin territory)
—Let people photo reply (another plugin territory, maybe related to BuddyPress since is like a PM)
—Let people answer this (same as above)
Video / Audio fields:
Like the current plugin, but also they have the option for using an uploaded file instead, or an external audio link that does not became hosted in Tumblr in Audio case. I guess it could be very used for Audio but not much for Video, unless one is using VideoPress or something, so a 'hook' may be done for those cases.
Chat fields:
They have a title field and a textarea without WYSIWYG editor. The chat is auto-formated on the front end by adding markup to the words preceded by a colon. This may be a 'theme' issue, yet the markup can be standard.
For example, when one types:
Tourist: Could you give us directions to Olive Garden?
New Yorker: No, but I could give you directions to an actual Italian restaurant.
it becomes
<div class="line odd"><strong>Tourist:</strong> Could you give us directions to Olive Garden?</div>
<div class="line even"><strong>New Yorker:</strong> No, but I could give you directions to an actual Italian restaurant.</div>
Not the most semantic but still.
Quote fields:
More or less like the current plugin, but a bit different:
—The actual 'quote' is put in a textarea without WYSIWYG editor, unlike the current plugin, which may be a good thing, although they generally don't need much additional markup.
—The quote textual source is put in a textarea with WYSIWYG editor, unlike the current plugin which used a single line text field, which may be a good thing, although it may solve issues like extending the context of the attribution a bit (like adding custom link markup and such), like another issue said.
—The quote source URL is put in the standard field for all post types. In the current plugin there is an URL field but only for Quote. I believe it could be used for most other post formats as well, even standard.
Link fields:
Same as the current plugin.
Text fields:
Same as an "standard" post. Since title is not present in all Tumblr post types and in the ones it appears is always 'optional', the title is always autogenerated based on the "body" field by default, which may be a good thing to implement in all post 'formats' (even standard) when a title field is absent or is omitted by the user.
Image fields:
Much like the current plugin, although it also have the option to take a photo with a webcam (which is very much territory for another plugin) and the option of link a Image URL from somewhere else, which at the moment of saving the post get saved on Tumblr. It may be a good option but a bit cumbersome to implement.
The URL field don't support "auto embeds" (like with Flickr), yet it may be easily done with WordPress (although not very easy to configure). When one uses the "Share on Tumblr" bookmark button on sites like Flickr the photo gets 'hosted' on Tumblr rather that just linked, like mentioned above.
Also, they have a 'click-through link' field to use a custom URL for when a image is clicked (when not used, it defaults to the full size image). When one shares a Flickr photo (using the "Share on Tumblr" bookmark button), it defaults to the actual link to the Flickr photo.
Photoset fields
'Photosets' are actually an image post but with more images attached instead. The post formats equivalent is 'Gallery'. Tumblr only supports 10 images maximum, which thankfully is not the WordPress case. Each photo can have a 'caption', yet that's already on core. A photo set can have a custom 'layout' from a list given depending of the number of photos, but that may be outside the scope of this plugin.
The 'click-though link' field is disabled in these cases, by obvious reasons. When one clicks an image it displays on a lightbox thing.
Tumblr also have "answer" posts (answers to PM messages), but they are outside of the scope of post formats at the time. 'Aside' and 'Status' don't have a clear equivalent on Tumblr besides the 'Text' posts.
Sorry if this issue became too long, yet I wasn't sure how to summarize everything coherently.
Is very likely the whole idea behind 'post formats' was inspired by Tumblr. That don't mean that Tumblr is an end on itself (they don't support titles for every post type, for one), yet still is a good reference.
Generic fields used in all Tumblr post formats:
—Site to post (a WPMU plugin territory) —Date of publish (already on core) —Content source (by now is only on 'Quote' post format, yet it may be good to use in all formats) —Tags (already on core) —Custom slug (already on core) —Send to twitter (another plugin territory) —Let people photo reply (another plugin territory, maybe related to BuddyPress since is like a PM) —Let people answer this (same as above)
Video / Audio fields:
Like the current plugin, but also they have the option for using an uploaded file instead, or an external audio link that does not became hosted in Tumblr in Audio case. I guess it could be very used for Audio but not much for Video, unless one is using VideoPress or something, so a 'hook' may be done for those cases.
Chat fields:
They have a title field and a textarea without WYSIWYG editor. The chat is auto-formated on the front end by adding markup to the words preceded by a colon. This may be a 'theme' issue, yet the markup can be standard.
For example, when one types:
Tourist: Could you give us directions to Olive Garden? New Yorker: No, but I could give you directions to an actual Italian restaurant.
it becomes
<div class="line odd"><strong>Tourist:</strong> Could you give us directions to Olive Garden?</div> <div class="line even"><strong>New Yorker:</strong> No, but I could give you directions to an actual Italian restaurant.</div>
Not the most semantic but still.
Quote fields:
More or less like the current plugin, but a bit different: —The actual 'quote' is put in a textarea without WYSIWYG editor, unlike the current plugin, which may be a good thing, although they generally don't need much additional markup. —The quote textual source is put in a textarea with WYSIWYG editor, unlike the current plugin which used a single line text field, which may be a good thing, although it may solve issues like extending the context of the attribution a bit (like adding custom link markup and such), like another issue said. —The quote source URL is put in the standard field for all post types. In the current plugin there is an URL field but only for Quote. I believe it could be used for most other post formats as well, even standard.
Link fields:
Same as the current plugin.
Text fields:
Same as an "standard" post. Since title is not present in all Tumblr post types and in the ones it appears is always 'optional', the title is always autogenerated based on the "body" field by default, which may be a good thing to implement in all post 'formats' (even standard) when a title field is absent or is omitted by the user.
Image fields:
Much like the current plugin, although it also have the option to take a photo with a webcam (which is very much territory for another plugin) and the option of link a Image URL from somewhere else, which at the moment of saving the post get saved on Tumblr. It may be a good option but a bit cumbersome to implement.
The URL field don't support "auto embeds" (like with Flickr), yet it may be easily done with WordPress (although not very easy to configure). When one uses the "Share on Tumblr" bookmark button on sites like Flickr the photo gets 'hosted' on Tumblr rather that just linked, like mentioned above.
Also, they have a 'click-through link' field to use a custom URL for when a image is clicked (when not used, it defaults to the full size image). When one shares a Flickr photo (using the "Share on Tumblr" bookmark button), it defaults to the actual link to the Flickr photo.
Photoset fields
'Photosets' are actually an image post but with more images attached instead. The post formats equivalent is 'Gallery'. Tumblr only supports 10 images maximum, which thankfully is not the WordPress case. Each photo can have a 'caption', yet that's already on core. A photo set can have a custom 'layout' from a list given depending of the number of photos, but that may be outside the scope of this plugin.
The 'click-though link' field is disabled in these cases, by obvious reasons. When one clicks an image it displays on a lightbox thing.
Tumblr also have "answer" posts (answers to PM messages), but they are outside of the scope of post formats at the time. 'Aside' and 'Status' don't have a clear equivalent on Tumblr besides the 'Text' posts.
Sorry if this issue became too long, yet I wasn't sure how to summarize everything coherently.