Linux's existance is because somebody had a personal itch, and it's grown to be something that is specifically free and well-engineered. It's difficult to compete with that on technological grounds.
I'm not sure what you mean by Google disagreeing with me; we have Java 1 system that is so ancient nothing works with it, an equally ancient Shockwave player, and an unusuably slow Gnash port, which doesn't support most Flash applets anyway.
As for how things could be achieved, the simple way of implementing threads which everybody else already uses and has been tried and tested seems to be the best choice; although it'd be a waste of effort anyway, regardless of how it's done.
MIPS has "hyperthreading", after a fashion. If it actually becomes a feature customers want, ARM may add it. But you can usually just throw another ARM code in the same package for a similar cost in complexity.