There's been widespread interest in such a thing, and hackers have been hard at work getting the operating system onto the HP TouchPad, for example. (Indeed, according to Liliputing, it's now possible to install Ubuntu, Debian, Arch, and Bodhi Linux on the device.)
Ubuntu may have lost its No. 1 spot to Linux Mint in DistroWatch's popularity rankings, but it's way too early to write it off yet. Canonical has plenty up its sleeve, I'm betting, and I'll report back as soon as I learn more.