What if crop sized sensors become better than the lenses?
They already are. The sensor used in the NEX-7, A77, D3200 is there today. Recent tests of the NEX-7 show that you need some serious glass to even come close to resolve all the sensor is capable of. At least $1000 worth of Leica or Zeiss optics.
While FF cameras certainly offer a lot, crop sensors offer their own benefits...they're far from the cut budget version of full frame many make them out to be.
Many DSLR shooters are videographers. The 1.6/1.5 crop is almost identical to Super35 and that's a good place to be at.
Many of these same shooters are also shooting with high end video cameras...many of which are adopting Super35 sized sensors as the new standard. Being able to replicate the DOF and feel between the two is very appealing. I've been told by more than one DP that the 5D is TOO shallow for some shots.
And those that are worried about the video race, don't watch what Canon (and others are doing), watch what the video lens makers are doing. As long as Zeiss is making cinema primes with an EF mount, you're safe. They're making E Mount cinema primes now...who saw that coming?
I like having the options of smaller lenses. While my L glass is sharp and amazing, my crop sensor lenses are smaller, lighter, and cheaper. With the exception of top shelf L glass, they're very good compared to most lenses.
I like crop factor. It can get a bit annoying on the wide end but turning a 400mm lens into a 600+mm lens is nice to have around for certain applications.
Megapixels can be nice in the studio but I shoot portraits with a 7D and almost always get more detail than I need, having to back things off in Lightroom so the customer can't count their own pores.