I think Linux enjoys a sort of "middle ground." It is not mainstream, nor is it dying out. I say this as a Linux lover who has Mint as his primary desktop OS and runs Windows under VirtualBox.
I don't think webOS can occupy that same ground. I think it's going to either really take off, launching to a solid #3 or maybe overtaking #2, but the "small device" category doesn't really have room for "middle ground." If the Samsungs and Motorolas of the world release a webOS phone, then I think you have something. If not, I think it will be a curious footnote within a few years. And I say this as a TouchPad owner and lover.