I think the Mini Velos would sell, probably not as well as a regular road bike, but they work well as a non-folding folder, if you know what I mean. Very portable. I don't have a need for one, there's no buses where I live, and I have plenty of storage space.

The retro city bikes are becoming really popular, and I like the way they look, but I'm a wuss, and I don't like 3-speeds. I might buy one of these for the wife, but I probably wouldn't ride it.

The Monster Cross bike: this is pretty much exactly what I'm looking for, and is what I'm riding now. I have a MTB converted to city use, and I ride it everywhere, on group rides, commuting, dirt, etc. If I were going to buy a bike, it would probably be a 29'er MTB/Cross bike with an extra set of road wheels. I could use this for literally everything.

(EDIT) In fact, I was looking at your Cliff 29.1 and thinking of converting it with drop bars and an IGH rear wheel. It would run me about $550 for the whole setup, which is half of what a disk-brake commuter sells for. I'd definitely use the rack and fender bosses.

Fat Tires: Very small niche, but there's a few hardcore Pugsley/Fatback groups who swear by them. It would be a tough group to get into, but if you can offer the same features for less money, I'm sure you'd sell some.