Vendor neutral anti aliasing with coverage information

Surprisingly a quick search didn’t turn up a suggestion. Sorry if this is redundant.

CSAA (NV) and EQAA (AMD) are great, but are not available to everyone.
Also, MSAA has a few shortcomings that are inconvenient for deferred rendering
performance (which even makes some AAA devs choose not to use MSAA).
Coverage information instead of replicated color samples would mitigate those
issues greatly.

I’ll just naively describe my needs in a typical deferred rendering setup. Note that
these are not met exactly by CSAA and EQAA.
-Small framebuffer -> few color samples (two would often be enough)
-Good AA quality -> n/16 coverage information per color sample

Shader support that would be very nice to have:
-Querying color samples and their coverage, instead of getting the same
sample repeatedly

A little off topic: Having the sample number as stencil would be absolutely great.

I expect that a lot of people will now tell me this is not realistic for a bunch of
good reasons that didn’t cross my mind, which I greatly appreciate.