[zanny]

> less useful releasing as open source would be.

Developers would find an immense amount of use in open sourcing their engines like this. It lets the community port them to every OS in existence including your toaster. A great/bad example is gemrb, which was an open source reimplementation of the Infinity Engine that almost certainly incentivized Atari / Bioware to let Beamdog re-release the games with modern engine updates across many platforms due to the free engine's popularity on mobile.

The open source nature of all the id engines is what keeps Wolf3d through Quake 2 games relevant this day. Their engines are bought to every new platform almost as a benchmark for porting software period, and you can play them effectively everywhere as a result. Compare that to abandonware titles like Blood that were their contemporaries, but never saw source releases and thus are effectively dead software that would only run on DOS.

I'd argue almost every console game release since the Xbox would benefit astoundingly from open sourcing their engine code. If we could see the APIs they wrote their renderers against we could reimplement them for modern cross platform tooling to enable native compilation and execution of games we still cannot emulate well because the hardware is similar enough to what we have now that we don't have the magnitudes of ghz to throw at it easily or often. And even older console titles would benefit, because they could be modernized with new resolution support, higher refresh rates, and modern rendering techniques.

This is all around immensely beneficial to developers because it is basically free money - people will keep buying copies for the assets even if they use much better engines you didn't have to put developer hours into making.