This would be awesome!

Just to touch on this very thing, as Garry posted on the main description of this mod, Mass Effect: Crucible is being integrated into the currently in development total conversion Beyond the Relays. I'm one of the project leads on that mod, and what you're describing is exactly what we are working towards, having both a free for all setup where everyone starts at the same level like normal Stellaris, and also having a purist map build which will have each empire owning each of it's colonies according to the lore, and having accurate fleets, empire relationships, etc.