I would definitely be interested in such campaign. Do I understand it correctly that there would be several races on Earth?
Yes, last time I had 5 initial powers on Earth, with a sixth added 10 years in. I was however, running them myself with some input from a few people regarding overall strategy.
I'd probably do something similar, but ideally have at least 1 person for each of the factions providing strategic direction and in return getting yearly reports. I might consider a more 'developed' situation, whereas there is some established infrastructure in the Sol system (kind of like Steve's NATO vs Soviet Union campaign, but with more factions).
As said though, waiting on 6.30, so much good new stuff that I couldn't bring myself to start something this big when I know theres an update lined up sometime in the next year (hopefully!).