The rumor sites have them bringing out two models - one a bit bigger and one much bigger. If anyone brings out an android nano I'll defect immediately (having been on iphone since day 1).

The Sony Z1f is a pretty great 4.3" phone. Which, sadly, is 'nano' these days.

And still larger and thicker than an iphone 5 (which is already a bit too big)

The Droid Razr M is about the same size, at 4.82 x 2.40 x .33 inches[1]. It's only .09 inches wider, and .03 inches deeper than The 5s, and it is actually .05 inches shorter[2]. I'm not sure if you'd still find that too big though.

1: http://www.gsmarena.com/motorola_droid_razr_m-4973.php 2: https://www.apple.com/iphone-5s/specs/

There are definitely smaller ones out there. Htc one mini. Galaxy s4 mini. ect.ect. 4.3 inch screens for both of those ones.

Both bigger than an iphone 5 in all dimensions.

Really looking for something with a hi-res screen, apple-speed touch latency, maximum but preferably smaller footprint than an iphone 4, and at least as thin as an iphone 5. This should be doable in 2014 and I think would be distinct enough without being ridiculously niche to have a reasonable market segment.

You aren't likely to get apple-speed touch latency outside of apple. They have worked much harder on this than everyone else and do a much better job of it. Sadly for you, I don't see them releasing something that small again. The 4S is still a decent phone, but you might have to settle for the 5 sized phones. Unlikely they ever release something smaller at this point.

Sadly the market doesn't love small phones any more - Sony killed their Xperia Mini and Mini Pro range due to lack of demand, which was a shame.