On IRC the developers have mentioned (as wishful thinking) a minimal (i.e. a stripped-down) version, with only kernel, drivers, and a few other small miscellaneous parts over which dedicated applications could run. This would be something for embedded systems and other specialized machines (basically servers) unlike the all-encomprising common version of ReactOS. That having been said, it's important to understand that one of the reasons for nano is... well, OS size, which for a "normal" version got to tens of GBytes! Currently, ReactOS is (and I think that's a lot --) under 200 MB with all its bells and whistles.