And still no one knows why x86 control registers are CR0, CR2 and CR3. What was CR1 supposed to be used for?!?

(This is actually true. I asked x86 architects when I met some).

According to http://www.pagetable.com/?p=364 (which also shows part of the reason the x86 needs so much documentation, by the way), it started its life "reserved", and never got a real role in life.

Sounds like someone meant to use CR1 after CR0, but someone bit-swapped the CR-number bus so you have to encode 4 in the instruction to get 1 where it needs to go.

Yes, but: "instead of overflowing the new bits into CR1, Intel decided to skip it and open up CR4 instead – for unknown reasons."

Sounds like someone took "reserved" a bit too seriously and/or couldn't figure out who had marked it reserved or why, and decided the latter was the safer option.

"We don't talk about CR1". ;-)