It should be possible to port glest to both android and ios and even chrome nacl.
The challenges are moving to opengl es2 and the networking. Of these, networking is perhaps most code churn, and there is a risk that despite streflop that games between arm and x86 don't work. But there is a good chance they do, and certainly they ought to be able to play other players on the same arch.
A touch-optimised ui (no rigght-click
etc) would be needed.
The big barrier is not code - its time and money. Developing for ios is not free, and all tablets need access to hardware