It's not that convergence is useless per se - indeed, the fact that both Windows and Android keep trying indicates that it's desirable.
But I think that any hope that this could come from the desktop Linux world, and be successful, was misguided, for the same reason why "Linux on the desktop" never happened at large scale (to all the people who are about to respond "it happened for me": sure, and I'm well aware of that - but that's not what the phrase actually ever meant, and we all know that). This is an even bigger problem with phones, because with the PC ecosystem, at least you can go around shopping for an alternative OS relatively easily, and common hardware is relatively open spec-wise. So something that has 1% market share on the desktop, will probably have an order of magnitude less on mobile.
On top of that, it's not enough to implement the base system. You also have to maintain it long-term, to port existing apps to it or write new ones, and to maintain those. Within the OSS model, maintainers are generally users. So the maintenance burden is high enough for desktop Linux as it is (because of relatively fewer devs/users, compared to OS X and Windows) - and then you throw mobile into the mix, which is an even smaller group. I just don't think it can work at that small of a scale.