With a crowdfunding campaign where large donations leads to requesting a
feature. I am pretty sure an hypothetical free software GTA 6 could be
entirely funded in this way.
Even without the fame of GTA's developers, Cloud Imperium Games received,
from about one million players, 89 millions to develop Star Citizen:
https://robertsspaceindustries.com/funding-goals
By choosing a license making the engine free software and authorizing
non-commercial redistributions of the whole game, they would have probably
got even more.
