> their decision to open source their game engines has so many implications that it is hard to even begin quantifying their impact

What are you thinking of?

As far as I recall, the main benefit has been to developer curiosity but I don't know of much impact beyond that. The games that used Id engines like HL or Call of Duty had to license it anyway right and didn't use the open source versions? I don't recall much of a scene around the open source engines unlike the mod scene that used the official game and assets.

Things like Quake2 running on the Quest uses an engine that I think started off with original source but eh, it's not that significant. Q2 was huge to me at the time but I can't muster the enthusiasm to play it in VR. I look at it briefly and I'm done.

There was Quake II RTX created by Nvidia but again, eh. That and Portal RTX did not make a convincing case for ray tracing. They ran like pigs and didn't look terribly good to me.