Huh?
I went into the aircraft files (opened in excel) and changed it so the X-Division version of the mig could be bought (alongside nerfing the ufo turn rate. I like air battles, but I'm not that much of a masochist) and it worked without issues?
This is a planned feature, yeah. It's already semi-supported in the beta.
Dagar - you now always have a "lifesigns" for each UFO and ground mission, and any alien you've autopsied will be recognised and appear in that list.