FWIW, the Next color machines had 12bit (4096) color and in practice it didn't make much of a difference. I was using one fairly extensively in the late 90s (by which time 24bit was the norm -- albeit not yet ubiquitous) and for anything other that photo/video work it was perfectly reasonable. It's amazing how far a good dithering algorithm can get you.
The refresh rate is, of course, a different issue