Re : Anyone using something other than jQuery and Zepto?

I think it would still be a good idea to formalize the API that CanJS relies on with something like Universal.js but only add implementations for jQuery, Zepto and a standalone version.

If anybody is interested in implementing another library there will be at least a testing infrastructure to develop against. 

I really like this idea. Avoid hard coding any dependencies as much as possible and leave the door open to those wishing to implement another base library. I think it would be a really forward looking approach. My 2 cents anyways.