Canonical is calling this Ubuntu for phones but even in their own presentation they mention it will run on tablet devices. Yesterday I said, on Twitter, that I was happy to see another entrant into this market. Android and iOS are not enough choices (though we've been dealing with Mac OS vs. Windows for years and years).
However, Gruber says that a gesture-based UI can never work. I don't know if that is true. I'd hate to say that anything is impossible. Gruber and I are old men. Maybe a gesture-based UI wouldn't work for us (though keyboard shortcuts come as second-nature to anyone my age and under) but will work for a future generation? What if every mobile OS became a gesture-based touch OS? Then humans would be forced to deal with it and get used to it.
So, I don't know if it is a non-starter because it is a gesture-based UI or if someday that will catch on as the norm, but I do know that if it isn't responsive or reliable than it won't take off regardless.