Please make an unambiguous list of the hoops Commons will be required to jump through before this feature can happen, so it's actually clear
Way to be acerbic...
list of these hoops, only vague generic hoops that apply to any kind
[..]
Like Aryeh said, Neil is currently working on a concrete implementation of category intersections. Only when that implementation is complete (or at least close) will it be possible to provide the definitive, specific and unambiguous list of requirements you asked for.
Not really. There are two main points 1) category deep tree traversal (flattening / deep indexing) at runtime is technically unfeasable. 2) automatic flattening produces nonsense results
Ok, lets's say Neil found a way to deal with 10. I give you that this is implementation specific. Number 2) however is independent of any implementation. Here you have your "hoop" (to to stick with your pejorative lingo): Get rid of the crazy category system and go atomic. What is vague about this, what part of this is unclear to you?