EF-S lenses, generically speaking from a marketing perspective, are aimed at the consumer market. Today's consumers vastly prefer zooms over primes. However, the 50/1.8 II is a popular lens (primarily due to its low cost), so I can see an EF-S 30mm or 35mm f/1.8 lens at some point - but for it to sell well, it will need to be cheap.
If Canon does release EF-S primes other than the 1:1 macro, I'd expect them to be low-end consumer grade lenses.