I really don't think so. Imagine every app with custom images / icons would need an update and this is way harder than updating iOS apps. The App Store is pretty "new" business and it is really fast but on the Mac it is kind of different. These things take longer.

Imagine Microsoft would need to release a version with retina graphics. This would take ages instead of weeks!

Another point is that it would cause fragmentation in the whole Mac / MacBook ecosystem.

I really don't think that this will happen in the next time!

An 11" with a 16:10 screen would be nice.