I don't want to be a wet rag about this, but...
While we can poll and speculate, I beleive Lionel will produce new locmotives in S that have already appeared in the O Gauge catalog AND the Legacy electronics will fit in.
It's a pretty tight squeeze in the U33C and the Pacific/Mikado tenders, so I don't think we'll see anything much smaller for now.
Pity, their CN 2-6-0 in S would be really neat.
Rusty