I'm so impressed that the two FE primes have t-stops matching their f-stops. I'd be extremely happy with a 35/1.8, the 55/1.8, and an 85/1.8. Those three lenses with t-stops matching their f-stops would be the tops. I'd also enjoy a pancake lens. How Canon has produced such a great 40/2.8 pancake for such a low price is beyond me. FE could use some cheap, fun lenses.
But forget all of that. What I'd really prefer is a 50mm/1.4 w/OSS. That would do me and I could be done with buying any more lenses.
Actually, what I'd really prefer is a set of lenses employing the Minolta STF optical apodization filter across an entire lineup of lenses. A set of STF lenses on the A7S would be pretty much the most exciting thing in the photographic world.