I think it's a brilliant idea !

By the sound of it however, this would take a rather long time at that scale and you need your own mod team:contacting all the teams, putting the stuff together...

How about starting with 3-5 mods with nothing too fancy in the beginning, I mean, if some of the mod teams decide to go with the idea I'm pretty sure they want to show off a little, just a hint at what it is, that sets their mod apart from the others,i.e. 4th Age or LotR want to implement some of their resized skeletons and new animations, NTW and Citadel want to show firearms etc.

I think therefore it would be better to start with a few mods, only showing off some models, to introduce the concept of this showcase to the mod teams and fans alike and then release updates with new mods and features, that way it's also alot easier to keep track of the work.

If you are in need of help I would do so gladly, I know how to make sprites and have access to 3ds Max for the purpose of making UI or fixing minor bugs.