Im not an expert, but the answer is not anytime soon. This is because Ubuntu Mobile has been optimized for the Atom CPU, not the ARM CPU of the tablets. Look at Debian on the tablets, its taken a long time to make it useable, and that was with an ARM port. Good new is that due to the open nature of Linux and Nokia's close work with the Moblin people, we will probably see benefits.

Just my 2 cents