Vincent: this was my initial idea as well. I thought it would be amazing to just have a tank that looks extremely simple, with just one coral in it. I'm a huge fan of tanks that don't define the aquascaping with rock, but with coral.
My initial idea with my small tank was to put a small rock in the middle, and grow a single acro. No fish. Just kind of like an art installation. All the biofiltration etc. would be in the sump, rather than in the display.
Ultimately fish, but ones that don't really care for hiding spaces as much initially, but do like to be in/around branches of an acro (chromis for example).
This is hard if it's your only tank, but if you already have a reef tank full of stuff, having one minimalistic tank sounds incredible.
I'm doing a small home remodel soon, and will be able to accomodate a much larger tank. I'll fill that one up with my heart's desire, but I'm going to convert my RSR170 into a minimal tank. Just three acros, or maybe just one magnifica in the center with a bunch of clownfish (we know how that one has gone though...). It could even plumb into the larger tank.
Either way, I think you should do it, especially if you can supplement all your other wants into a different tank
My choice for an acro? Probably a pearlberry or something similar.