But even with the situation now, aps-c has many advantages (longer reach, affordable good ultrawides) so that it'll stick around for some time to come simply because smaller sensors will keep being cheaper as larger ones. The Rebels will loose market share to mirrorless, but many people like me won't want to use an evf even if it's a good oneTo take that a step further, the people that use APS-C at the upper levels (think 7D) are people like birders, sports guys, and nature photographers. Few if any of them would adapt to a M4/3rd camera because the EVF and AF limit them in all of those situations. Can't shoot sunrise or sunset shots of animals, because your EVF is dark and hard to see. Can't shoot birds or sports effectively because the AF is too slow.
That's not to say 4/3rds cameras won't solve some of their issues, they will, but there are some pretty major hurdles to climb to cover those use cases. And until they solve them, you won't see APS-C go away.
Also why make EF-S specific primes when Canon can make EF ones, which work for a MUCH broader audience, and when those lenses are pretty small anyway (if the 50mm f/1.8 and 35mm f/2 are too big, get a P+S). They only make EF-S lenses to solve a specific APS-C problem, like UWA (10-22), a high quality lower light zoom (17-55), and light-weight zooms (55-250).