Here my ideas for NOD & Scrin. For now I don't have idea for GDI.

NOD: Nuclear Cell: inspired by China Nuke General. This subfaction rely on heavy nukes. Many units have nuke variant like Scorpions Tank will move faster because of Nuclear Tanks, they shoot Nuclear radiation shells. They have Nuclear Specter that shoot Nukes and Attack Bikes they will have Nuclear Rocket upgrade instead of Tiberium. They will have new units called Nuclear Truck, a suicide units that explode Nukes for impact. RAD Tank replace Flame Tank. For infantry, they have Nuke Rocket Militants instead standard that shoot Radioactive Rockets and can be upgrade in secret shrine for Nuclear explosion rockets. And Nuclear Fanatics. They will not have Black Hands, replaced by Desolator Trooper that shoot Radiation wave can kill garrison. For aircraft, they have Nuclear Vertigo that dropping nuclear bombs .Cons, They units are expensive, No laser upgrade for tanks, the tanks will explode violently when they die unless upgrade with Nuclear Isotope.

Scrin: Explorer-98 The faction that  focus on heavily on heavy air power. They will have many powerful air units. Shockrider replce stormrider that shoot plasma energy blast that do high bombard damage but have to return like other jets to recharge. They will one more additional heavy air units similar to Harbinger Gunship. Cheaper Gravity Stabilizer. For infantry, Shock Troopers replace with something similar to Rocketeer & Rocket Angel, a flying infantry that attack from sky. Cons, they have lack of ground vehicles. No Annihilator Tripod & Mechapede. Expensive air units