I (naively) hope that eventually people who prefer microtransacions will realize what a waste of money it is, and start paying upfront. But seriously, maybe a good solution would be to design the in-app purchases in a game so that instead of endlessly paying for consumable items, one would pay for actual game features. That way, you can play the basic game for free, and then start "constructing" the full game piece-by-piece by purchasing individual features. For example, an RPG where you can play the warrior for free but then pay $X each for additional characters. Or a "dungeon-keeper"-style game where you can pay to unlock more types of monsters and tools.