Some more details:
1) When you want take some alien vehicle you transform into this vehicle and cant get out.
2) Scrin heal in tiberium fields and near extractor.
3) (optional) Make dropship model which one randomly spawning in all maps and scrins arriving from these without respawning ability, and some players randomly transfering to sctin side. It arrive in random time (not early 20 minutes!)
4) Superweapon will be mother ship beacon - this thing slowly arriving and charging, and do big as crap KABOOOOM!
5) Only 1 annihilator maximum allowed and it will be cost 5000
6) Defilers heal all scrin vehicles if shhoting at them, while infatry love more solid tibetium in fields
7) Shock troopers now have busser granede which is cleaning area near unit from 3 enemies on foot.
8) Scrin take 30% of server players just because they fat
Other details be added soon to make thi concept more detailed and playable.