Linus is a kernel hacker, and already busy tending to his own project.
"GNU/Linux" is effectively a committee of communities, with sometimes conflicting goals. It took Canonical and Valve to put things into shape on the desktop, and that's mostly because desktop was becoming less relevant.
I see two ways for things to change here:
- A massive, for-profit corporation, someone willing and able to challenge Google and Apple on an even ground, is hell-bent on making a Linux-based phone (Microsoft failed even after acquiring Nokia);
- Another platform shift happens, making smartphones irrelevant in comparison (think: when smartphones displaced desktops).