Whole microtransaction market generate quite a big heap of money.
Trick is to make it
lucrative. There are enormous amount of competitors in this market, so you must made something truly outstanding, evolving and simultaneously stimulating to generate decent cash - or make something simple, boring and unrewarding, but
heaps of it.
For me, it's quite impossible to individual. Company can afford to make a metric ton of crap "free to play" games, having little income from any but big cash for everything. Person cannot afford to do that due labor/time constraints.
So my opinion: go to mobile market for quick profit with simple games.