Not while maintaining warranty...

Quite.

It is unlikely, unless the physical size of the drives match.

Taking Karmas to pieces is definitely not as easy as taking car-players to pieces (at least if you want to put it back together again neatly). But I suspect, if this entirely new drive form factor takes off, bigger capacities in the same physical sizes as the initial 20 and 40 will eventually become available -- much like the way that 2.5in drives used to come in 16.5mm and 12.5mm heights, whereas now even the biggest capacities are 9.5mm. Of course, in that sort of timeframe Rio is hopefully going to have entirely different and even more wonderful players for you to buy...

Peter