Old and OT, but i'd like to chime in on the issues
- Generations' VM code is based on the Q3A SDK, which has a strict EULA that prohibits use on anything but a retail copy of Quake III: Arena. You'd probably have to "cleanroom" it on a new GPL codebase, and that would require lots and lots and lots of time.
- OA doesn't have "same name" equivalents for models used by Generations so dependency on them would render the mod unplayable.
- id intellectual property is used anyway, so for a real "OA Generations" you'd have to redo it all in respect to the other free equivalents, like FreeDoom and OpenQuartz (worse, there's no Free equal for Wolf3D or Quake2 in existence). This would be huge effort for little benefit.
- On top of that, since Generations derives from Q3A content for most things like characters and the menu system, you can't legally play that in OA
- As mentioned already, selling Generations is legally impossible. Suggesting unauthorized commercial exploitation is a nasty idea.
It's kind of a shame anyway since OA has some excellent remakes of Quake DM3 and DM5 based on the released open-sourced GPL map files. Playing them in Generations is one of the reasons why i'm taking them out of the baseoa paks into their own tribute pak as a GPL-licensed addon for both OA and Q3A.