Had an idea I thought would be interesting, so I figured I'd go ahead and post it here.
Using the basic, vanilla kernel, set up a series of USE flags that list diffrent patch(sets) for the kernel, and allow a user to set them accordingly to bring in those patchsets.
This would cause some serious problems with alot of people who would try and pull in competing patches, but it seemed like an interesting idea when I started to think it over.
Yeah, that wouldn't work... That's why we have separate ebuilds. :)