Now that we have ultra-cheap mass storage, in the form of CF memory modules, and now that there are 805x versions at speeds of 100 MHz, it might warrant a look.

At low volumes (the only place an OS for the '51 could ever even be considered) using "805x versions at speeds of 100 MHz" would cost you a lot. [of course, there is also a higher cost at high volumes, thus it would not even be considered where the "cost penalty" really matters]

Erik