It seems to me that Coinbase alone could decide to make a URSF defacto "popular" whenever they wanted to - and the majoriry of miners would almost be certain to follow. It would be at that point that BIP110 users and miners - presumably still in the minority - would have to choose whether or not to continue on with the new coin they have created. I would be shocked if more than a handful of BIP110 supporters (especially any would-be miners) would be willing to die on that hill.