They are disabled because I couldn't make them work the way regular render elements work. I can share the details, but basically I couldn't put pixels into elements bitmap buffers. So I decided to disable them to prevent Max from saving empty buffers. Instead the plugin tells appleseed to save AOVs by its own means using file names from the list of elements. I tried to save different AOVs and it worked for me. Here is a CGTalk thread with details of my issues with render elements: https://forums.cgsociety.org/t/sdk-custom-render-element-cant-access-elements-bitmap/1912359
According to @usakhelo on Discord: