In all honesty, I highly doubt we will be doing that any time soon, simply because of a few things.
1) Unlike Desktop, MCPE worlds have a limited space. Meaning, the world is only so big, and it doesn't create more and more parts of itself to expand.
2) The sheer amount of lag that would result from so many mobile phones connecting to that would be crazy.
3) Obviously, MCPE is still in it's "alpha" phase. There's just not enough content in the game, nor enough open gameplay to make multiplayer completely worthwhile.
It would be amazing if this were possible, but unfortunately, mobile phones are still in its infancy in terms of gaming power.