Where are today's games with sufficient insight on their technical aspects, to the level we got with Commander Keen, Wolfenstein and Doom?

Dwarf Fortress solved some outstanding lag issues involving tracking owned objects. But if you ask a random person HOW, we don't actually have a serious clue.

Think of well known instances of big developers having their code exposed and we have... I dunno, Valve's TF2 leak and their incredibly rare Dota 2 between the lanes posts?

There is no John Carmack now. You're saying its because there's no large space to improve on like how early people had to. I say it's not because the struggles and unique problems disappeared, but because there isn't a benefit to that type of transparency anymore.