What kind of sole/tread do they need to have?

Oops, forgot to include that requirement - the sole needs to be grippy somehow or other. The boots I currently use have felt soles, there are various heavily lugged options also. I think if my feet have more mobility, the grippiness of the sole will be less important because I won't be teetering on slimy rocks with 1 square cm of contact! This is why I initially thought of kayaking booties - they're presumably designed for walking on slippery surfaces once in a while.

Did you see the boots mentioned in this question here? http://www.toesalad.com/questions/mini-mil-boots/

I wonder how they would work?

Hm, the mini-mil boots look promising, although they look at bit too high - my chest waders have built-in gaiters (e.g. http://www.simmsfishing.com/shop/waders/womens-headwaters-stockingfoot.html ) that assume you're using their just-over-the-ankle wading boots (e.g. http://www.simmsfishing.com/shop/footwear/freestone-boot-felt.html ).

This is my complaint with nearly all the more hiking boot-like minimalist shoes - they're so tall! It'd be nice to have something over the ankle to protect those nobbly ankle bones, and keep some duff out of the shoe, but I don't want something halfway up my calf. Straying off-topic here...

I'm not sure why the fishing community thinks having a great heavy rigid slab on your feet is a good thing. I've got my feet stuck between rocks a few times when I slipped between them because I couldn't tell what I was stepping on. Not a big deal in a small stream, but very dangerous in a fast-flowing river. I've appreciated the hard boot when doing kick samples (as the name implies, kicking the rocks on the bottom to dislodge insect larvae) but I could still have at least some of that protection with a more flexible sole.

Long rambling answer to say, close, but not quite there!

Too bad the VIVOBAREFOOT boots and the Inov-8 boots are all waterproof, I think they would be a good height but they certainly won't drain. The only other possible options I can think of are the Transition boots from Sole Runner http://www.sole-runner.com/barfussschuhe_comfort_line.htm or perhaps the Merrell Proterra Mid http://www.toesalad.com/reviews/a-review-of-the-merrell-proterra-mid/

Well, I was in the field recently on a hot day in shallow streams, mostly bushwhacking, so I ditched the waders and wore my Merrell gloves. I still don't see the benefit of a stiff sole, but I could really have used some toe protection. I felt more sure-footed, but my feet would still slip down between rocks, and by the end of the day my toes were feeling a bit mashed. Fine the next day, but still...

So now I want what I'm certain doesn't exist: a minimalist over-ankle quick-drying boot with a hard toe-cap. Dream on! I guess I'll just have to wear the wading boots and try not to sprain an ankle.