FLOP talk:Improve mesa handling
While, technically, you can make mesa ebuilds installed into slots by power of portage, this will not make good results as you will need to fix quite a bunch of packages's build system to have the ability of building against slotted versions of headers and libraries, this doesn't seem achievable in reality.
(Comment above from Oleg)
I'm interested to figure out the dependency situation first. Then work down from there. How should packages that depend on mesa work? Can we have backwards compatibility (as Oleg points out, rewriting all mesa-dependent ebuilds would be a lot of work. Not impossible, but great to avoid if we can.)
I'd also like to start actually documenting the specific conflicts in this FLOP, so we can see the particular issues and then look at ways to address them.