It would take a frak load of work to do everything that would be needed for it all but that’s why you’d split it up into components and subcomponents, start by splitting it up into graphical requirements and mechanics requirements and then make it so both are interchangeable. You could start with what amounts to a factions, just reskins really with a couple of minor class changes or the like to mix things up, move onto larger things like large scale class and structure rebalances to make them a separate race. Meanwhile you could also be developing components that would be integrated as they get made to allow for the more advanced mechanics that would be the really good part.
I decided that with this post it was starting to get a bit off-topic so I’m starting a new thread relevant to an actual mod. Link to thoughts is here.