I'll have to see, Kalos has a lot of girls and not many legends, so getting all the humans in might be tricky
Viewing post in The Legendary Pokemon Breeder - PART 2 - ABANDONED comments
A possibly (horrible) great idea:
You see how Zygarde (and a couple others) have different forms?
The idea is to get them partially to unlock a girl and then fully for another one. Example: Zygarde 10%, 50% and 100%, Hoopa/Unbound, Diancie/Mega
Either that, or have one of the previous legends gain their mega/primal and with that unlock someone