Wrtiing is on the wall
"No need to suggest forking Android, AOSP already is that 'fork'"
No it's not. While Google were trying to play the open source game they were keeping this pretty fresh and up to date. This was good and devs and hacker were always working on current code.
Now Google are saying they are "not releasing source for the foreseeable future". This it then a different game altogether. AOSP will still be Google, it will be updated to Honeycomb at some point but by then devices will have been out for a long time and people will be left working building on old code base. While AOSP is always way behind production devices and versions given to preferred partners, AOSP becomes very much a send class product. always kept behind google partners and 2nd class. This is NOT how it has been to date.
That is why a true branch would be better, as it could grow independent of Google and produce an open source version that could compete with the google offering and judging my some of the work on XDA, even better!
You can kiss good buy to great roms being better than those on production manufactures devices it google are going to start keeping the base source back.