Apple's and Google's (and Microsoft's) platforms already contain web browsers. The "web platform" already exists on every relevant device sold on the planet. The only variable is to what degree each browser implements web standards.

The biggest missing piece of the puzzle is a webapp store that enables distribution, promotion, and monetization. And you don't even need a native app for this, as the "webapp store" could just as easily be a web page, thereby surpassing e.g. Apple's and Google's 30% cut (what are they going to do, block the web page?).

It's a long shot, but if Mozilla can pull it off it would be a huge leap for openness and consumer choice.