Report: Successful install on 2011 iMac
iMac12,2 2.7 GHz Core i5-2500S, 12 GB RAM, AMD Radeon HD 6770M 512 MB
Install to Firewire 400 disk formatted as APFS worked, but wouldn't boot. I got the no symbol. I didn't try reformatting it as HFS+. So I created a new APFS partition on my internal drive and that worked. (I love how easy this is to do via APFS.)
Initial impression:
System was very, very, very slow during setup and early use. It seemed to progress to just being slow after a while.
Youtube HD videos play correctly in Safari.
The News application is interesting, but content is too dense. It needs more white space.
Chrome seems to work OK.
Problems:
"Automatically adjust brightness" doesn't work.
Lots of video tearing when moving windows, many windows don't redraw until they take damage.
Lastpass application crashes, lastpass Safari extension doesn't work until you restart Safari.
Home application won't launch, says that it's damaged or incomplete (?).
So kudos to dosdude1 for getting this to work at all, but while it's interesting to play with it's really not usable for day to day use.