Hello.
I've been working on mixed crew mod - basically Aliens eventually figure out, that their races strengths lie in different places, and they try to compensate each other. Like they do in TFTD. After roughly half a year you would start getting mostly Mixed Crew Ship. Mutons are mostly soldiers, Sectoid Medics, Leaders and Commanders are Ethereal, and anyone (except Ethereals) can be Engineer or Navigator. Terror weapons are Cyberdisks and Sectopods. (Perhaps in next version I'll make Chryssalids appear in terror missions)
Issues caused by engine limitations:
If one alien or given rank is of specific race in a given ship, all aliens of this rank are of same race on this ship.
Even if you hyperwave decoder reports that Small UFO scout is of hybrid crew, there will still be only one alien in it.
(there are probably ways to work around, but it will take too much time)
https://www.openxcom.com/mod/xcom1-mixed-crewhttps://www.openxcom.com/mod/mixed-crew-and-tasoth-commanders