Of late, I've come across two things that would make great wiki pages.
This thread is mostly for me to keep track of those things to either ultimately write them or ask for them to be written.
Right now, the wiki is in "OK but not great" shape and the long-term
The first is documenting the RAM speeds in Wombat motherboards.
In particular: What is the RAM speed on the Quadra 800, Q650, and 25/33MHz C650s.
The second is information about booting from USB on PowerPC Macs.
In particular, what models can boot from USB, what OSes can they boot, and if necessary what commands are needed.
Older, but also relevant: Mac hardware and OS disk limit information and testing.
Most of the information is gathered, but it would be nice for it to be a page rather than a post in the middle of a thread.
Added 2019-01-26: What Macs can boot OS 9 (stock/default).
Added 2019-04-04: IIci/IIsi video output system, support for 640x480@60 or no.
I still haven't played with the Pages functionality, but we do have it.
Please feel free to add more ideas especially if you see forum threads that should be captured or rewritten as articles or anything that doesn't exist yet but would be good reference information.