My comment (below) can be directly linked to here.
As mentioned above, the larger “framework” themes are likely to be around for a good deal of time, but what of the other themes in the repository?
I do not believe there is a theme (anywhere) that cannot be made into a “parent” theme with a child theme created from it, but who will manage these parents in the repository? and for how long? Also, must the parent reside in the repository for the child to be housed there as well?
Perhaps a second repository for child themes of specific frameworks? The framework author(s) would have to submit their theme for special approval to be included in this “new” repository … perhaps as part of premium services?!
Just some thoughts …
My vote: undecided.
As I wrote July 23, 2009 child themes can and do exist in the theme repository. Desk Mess Mirrored and Shades both contain a child theme folder in the compressed file currently available from the WordPress Extend Theme repository (see my themes here).
Will child themes be available from every theme inside (and outside of) the repository, or will they only be accepted from a select clique of “frameworks”?