Perhaps Themes (and plugins) that don't work in vanilla 2.1 or above just be deleted from add-ons ..
as a first step in doing something about the add-ons section. Revamp of addons has been discussed for about 3 years ago, but since the add-on project is so big, it will likely remain in inertia forever if little steps can't be made.
e.g. burying or moving junk or non-working add-ons with current stable vanilla version out of the main add-ons.
Many are probably so far gone, working from the old framework wouldn't even be worth the trouble.
On the same note should individuals be requesting and begging that certain plugins work with 2.2 (while it is still in beta mode) and barely out a few weeks. I would think it should an rc before developers get pestered about workability with 2.2BETA
might keep the add-on clutter down, as well as the repetitve pestering for addons to be upgraded that never will be and will never work without major overhauls.
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.