Mass effect RTS would work amazingly. Think about it. (Wishwork activated)
Set 50 years after ME3, the galaxy is erupting in civil war after the state of galaxy was shattered by the reapers. All of the major groups have given their all to become the dominant force of the Galaxy. You got at least 4 viable races.
Citadel Forces- With Asari, Human, Salarian, Krogan, and Turian fighters. and all round team
Veil forces- The Geth and the Quarians. Best tech, slow startup but becomes deadly endgame.
Terminus systems- Lead by Aria, You have the 3 main crime gangs+Batarians. Deadly at the beginning, but doesn't advance much
Reapers- Use different types of Husks, Scions and collectors to fight. Gets massive super units and mobile bases+Converting dead enemies, but slow and fragile units.
Zealots- Hanar and Drell who want to convert the entire galaxy, after seeing the reapers arrival as part of some divine prophecy. Fast and most units can stealth.
Humans- Cerberus + Human rebels. Got strong Reaper tech. Weak units, but MANY different Commandos/Hero units.
Gahns- New race that discovered Mass Effect fields after repelling the reaper invasion. Each one is 12 feet tall and could match a Krogan. Believes Citadel responsible for their home-worlds attack
Element Zero for Hero units/upgrades.
Metals for normal units
Money from defeating creeps
Volus Shopkeepers, that sell upgrades to bases (i.e short term shields, hero items)
Unique commanders for each race with unique benefits (I.e The Veil could get Tali and Legion, while the Citadel could get the Turian councilor, who can destroy armies every so often by refusing they exist.
Mercenaries for hire, cost a lot but stronger than most Hero units. Includes the child of Kasumi, Biotic Commando Liara and more.
DOITBIOWAREDOIT!