TL;TR: the RO Bundle may consider relying on the "Packaging on the Web" work on long term, rather than on UCF.
The longer story: the W3C Web Application Working Group has begun working on a Web Packaging format: "Packaging on the Web". The goal is to define a browser friendly packaging format that may have many different usages, you can see some examples in the document itself. Technically, it is fairly different to UCF insofar as it relies on multipart MIME, i.e., based more closely on Web Technologies (primarily HTTP) that all browsers use routinely. It is expected/hoped that browsers will, eventually, include (un)packaging natively. Combined with the ongoing work of Service Workers this may become a very feature in the future. However, the document is only a first draft, the work on packaging format is still at the beginning and, actually, put a bit on hold until the spec on service workers becomes more mature.
An RO Bundle is very much bound to the Web, i.e., to browsers. Hence it may be of importance for the work on RO Bundles to at least consider that alternative. Even better: RO Bundle may be an important use case; by submitting it to the Web Application Working Group the RO community has the possibility to influence its final shape. As far as I can see, the core of RO Bundle is not bound to the packaging format, so it would not require a major change as for the technical work.
Note that similar issues may come up for EPUB. The W3C and IDPF is working on a White Paper "Advancing Portable Documents for the Open Web Platform: EPUB-WEB" which may expand into a new version of EPUB, eventually. One issue that must be considered is whether there should be a move towards Web Packaging (or not). There are already discussions in the Digital Publishing Interest Group at W3C, and there will be a F2F meeting in a few weeks where this issue will be on the agenda. I think, on long term, it may be very important for the work on EPUB-WEB and RO Bundles to converge in some sense; after all, scholarly publishing is a major area of concern for all...
TL;TR: the RO Bundle may consider relying on the "Packaging on the Web" work on long term, rather than on UCF.
The longer story: the W3C Web Application Working Group has begun working on a Web Packaging format: "Packaging on the Web". The goal is to define a browser friendly packaging format that may have many different usages, you can see some examples in the document itself. Technically, it is fairly different to UCF insofar as it relies on multipart MIME, i.e., based more closely on Web Technologies (primarily HTTP) that all browsers use routinely. It is expected/hoped that browsers will, eventually, include (un)packaging natively. Combined with the ongoing work of Service Workers this may become a very feature in the future. However, the document is only a first draft, the work on packaging format is still at the beginning and, actually, put a bit on hold until the spec on service workers becomes more mature.
An RO Bundle is very much bound to the Web, i.e., to browsers. Hence it may be of importance for the work on RO Bundles to at least consider that alternative. Even better: RO Bundle may be an important use case; by submitting it to the Web Application Working Group the RO community has the possibility to influence its final shape. As far as I can see, the core of RO Bundle is not bound to the packaging format, so it would not require a major change as for the technical work.
Note that similar issues may come up for EPUB. The W3C and IDPF is working on a White Paper "Advancing Portable Documents for the Open Web Platform: EPUB-WEB" which may expand into a new version of EPUB, eventually. One issue that must be considered is whether there should be a move towards Web Packaging (or not). There are already discussions in the Digital Publishing Interest Group at W3C, and there will be a F2F meeting in a few weeks where this issue will be on the agenda. I think, on long term, it may be very important for the work on EPUB-WEB and RO Bundles to converge in some sense; after all, scholarly publishing is a major area of concern for all...