Probably #3. Much like game consoles have competed against each other for several decades. Seems to be a very good comparison. Most of the big titles will be cross platform, some tiles will be paid exclusives, with lots of smaller games targeting one or the other until they reach some critical mass of success that justifies going cross platform. It's going to be a Columns/Tetris -- Mario/Sonic sort of world but not just for games -- applications too.