[taiki]

Not unprecedented though. Carmack did once advise Ken Silverman on using sectors with his 3D engine. Which later became the Build Engine.

[z3phyr]

Correct me, Build engine is 2.5D. Isn't it?

[taiki]

The exact nature of various FPS gaming engines from that era kind of gives me a massive headache.

Still, the point stands that this isn't unprecedented. John Carmack's has, in the past, just helped out potential competitors before.