Put me down for crop frame cameras being a future oddity from digital's beginning. Sure sensors will get better, and some will get smaller but i would think that larger will always be better in many ways, except price. And that's why they were made, so people could actually afford a dslr. And the high end ef-s lenses desings are pushing forward! that's sillly. Besides it's not like crop frame cameras are exactly small little pocket models, that's what mirrorless and cell phone are for. I've got an old 1/2 frame 35mm film camera perhaps from the 60's, i can't recall. One day the 1.6 crop dslr will sit next to it on my shelf.
Without 2 sensor sizes and 2 different mounts, camera manufacturers would need to come up with some new (and yet equally convincing) way to sell 2 or 3 distinct tiers of lenses, then, or else they will have to lower the prices for acceptable IQ telephoto lenses. Every consumer, even the casual ones with small budgets, expect to be able to shoot telephoto. Period.
EF-S Lenses: The fact that EF-S won't physically fit onto the FF bodies helps keep the lines separate, and preserves the perception/illusion that the a gi-normous price difference is fully justified. They would have to make decent affordable super-telephoto EF lenses that were not "L" lenses or else the competition would murder them. And they would have to be 1.5 or 1.6x longer than their competitor is selling, but for the same price. Once they do that, though, I am not sure that a red paint ring and a metal exterior alone would be enough to keep the two separate in the minds of consumers
if the prices are so wildly divergent. I think without EF-S lenses, Canon would feel more pressure to lower the prices on its L lenses as a result of the loss of product differentation.
Crop bodies: If one company (Canon or Nikon, or whomever) unilaterally chopped the end off of every lens in its lineup by eliminating the 1.6 (or 1.5x) telephoto boost of a crop body, it would be handing its competitors its own head on a plate, ceeding all its mainstream consumer/entry-level prosumer sales to the other guy. No new customer would buy into a line with inferior telephoto offerings at the entry-level price point as compared to what its direct competor is offering. Merry Christmas Nikon! Not only are lower-end buyers much more numerous than the elite few, but an appealing entry-level system of lenses and bodies is the only way to get new customers to buy into the Canon line. If there was no staircase to climb up for a beginer, but rather a sheer cliff that takes $5,000.00 to 10,000 just to get started, then your customer base would basically stop replenishing itself, and the brand would whither and die as its existing customers all age and die off.
Just my 2 cents...