They will not.
1.) Not everyone can possibly afford an $8,000.00 camera, nor a $3,500.00 camera.
2.) Canon sells many many many many more crop units than FF units.
3.) It would strain consumers' credulity beyond its already thin limits to have a range of all-full-frame cameras that vary in price between $500.00 and $8,000.00, so they would keep the two sensor sizes for that reason alone even if there were no other reasons. The 2 different sensors camoflage the crazy markup.
4.) Very few hobbyist bird watchers/high school sports fans could or would pay $13,000.00 for a lens, and the 2x Teleconverters
kind of suck leave something to be desired. So without crop-sensors, you are basically screwed for birds and any other far-away subjects unless you are ROLLING in the excess cash.
I think sensors, like CPU chips (and everything else), will continue to improve while simultaneously getting cheaper and smaller at a quick pace. If anything I can expect to find higher-quality smaller chips in the future. Smaller chips would both cheapen production cost AND provide the largest possible numbers of consumers with access to 400mm and 500mm and above for a price they would be willing to spend.
While I realize that would be crimping extreme wide-angle shooters as it kissed long-shooters on the lips, consider how much more most people value telephoto over extreme wide-angle, and also also consider how much easier it is to stich photos togehter to make good wide-angle landscapes/etc., than it is to try cropping out to telephoto lengths without destroying the IQ.