> Good luck getting a publisher or platform holder on board with that.
Yes, this is the long-standing problem with software freedom in general; not specific to game publishers. And I don't expect that to change any time soon; I'm hopeful for the indie developers.
But a recognized problem in our community is the inability to compete with games with multi-million dollar budgets; it's simply not possible at this point.
If you ask indie developers you'll find they're more concerned with paying their bills and building enjoyable games than opening up their software(and 90% of them use GameMaker, Unity or other platforms).
Like I said, you don't really have a good grasp of the industry. 9/10 indies don't make it, and none of them make it to the level of Notch. I'm talking about people who know what they're doing, burned all their savings from BigCo so they could work for ~1.5 years and still didn't make it.
Open source software is so at the bottom end of the scale, and you already have a bunch of frameworks out there if you want to know how the nuts & bolts work.
Seriously, there's enough barriers to being successful in gamedev as it is, I don't see any reason to add another one on top of that.