I remember the mixed race mod, I used to use it, until I realized that everything had equal race weights to the vanilla aliens, which meant that when adding gazers/waspites/anthropods to the mix they had very low odds to shop up.
Using them specifically as a warning is what I find particularly interesting. It's like the aliens start producing/using these, send the first batches as elite elements/test cases, and then put it in mass production. You can slowly realize you're in trouble instead of always seeing sectoids and floaters until the day ethereals and sectopods decide to drop in on a city near you.
Anyway, i just had the idea to combine in the future, Hobbes new Special Mission, like Facility Attack, Facility Defense etc.. with the Missiontriggers for additional alien missions in my Mod. At the moment i am only calling in additional vanilla missions, with a limit of 2 of these Missions per Month.
But pulling in these new Missiontypes over those Missiontriggers and give them a specific Name/Briefingtext, like "UN Counsil - urgent request" could be really cool, think about the Counsil Mission from Xcom2012.
This actually would be something similar for OpenXcom to some degree.
I personally like the Idea, and you?