Well, i have given this sort of thing a thought lately since the 'Total Conversion(s)' upgrading of X-Worlds' 39 races is on my working schedule.
Going from custom races to a real RaceConfig.xml file (in fact, i plan to have MORE than just one central file) requires to edit the whole set of default races (00-TA to 11-KR *and* the bottom Minors) and replace all values with my stuff. And that's where it hits me; scribbled somethin' on a post-it and forgot about it for awhile.
So, yesterday evening (as i was done with some of the inserted techs in the XW-tree) i came back to the "idea".
Akilians are Number 13, right... what stops them from being one the missing three remaining major races if you (as either a custom or a major) plus the maximum of 9 opponents roaster is filled up -- Nothing but their gameplay status and general interface surroundings. No UP meetings, not even on Graphs! So what.
...and yet the xml definition lines remain basicly the same process for all except for the Portrait, Logo and race number and a few negligeable items.
So there -- **make** a Drengin out of a Snathi and a Korx with some Paulos and you've got yourself a context which mimics a full 12 races built off the usual Nine Majors with three Half-like-Majors.
Abilities changed with the originals, Ship styles, dialog tags, etc. The illusion could be almost perfect.
Mind you, i haven't tested this. It could be fun to try though.
Otherwise, a huge amount of re-coding work would need to be done by SD that not even a kinky unstable external patch would adress.