Looks like it'll be Gaians on difficulty 4 currently, so assuming we don't get any last minute votes how about some extra rules? Essentially if you want me to do one these post to cast a vote for it.
A) Respect the fungus! Absolutely no fungus removal, in fact if I deem an area low on fungus I shall plant more.
A)i) No forests! Forests destroy the fungus when they spread, to preserve planets ecosystem I must minimalise my impact, thus I shall refrain from introducing earth plants in an uncontrolled manor. (This one is likely to make the game a lot harder as forests are pretty much the tile base improvement being quick to implement, they give minerals energy and nutrients and with a tree farm give enough nutrients to support the worker working them.)
B)Respect the wildlife! Absolutely no attacking native wildlife unless it is absolutely necessary., so while I can attack mind worms that come near my base and threaten my formers whilst exploring I'll have to detour around them.
C)Zerg Mindworm rush! I can only use mindworms/locusts/isles as attack units, my bases can be defended by normal units but when it comes to offense it must be mindworms.
D)i)No War! We love peace and flowers and peace. War is never justified! I must always accept any equal terms peace I'm offered and attempt to negotiate peace, no declaring war.
ii) Kill the defilers of planet! The exact opposite, I must fight tooth and nail to protect planet, if I'm not in a war then I must immediately start one (I'll cut myself some slack for the first few turns mind you). Peace can only be accepted when they fully surrender.
E) No nukes! Planetbusters harm planet too much, I must never build them.
So if any of those appeal to you say so, also feel free to throw in your own better ones but try to make them logical for the Gaians.
EDIT: Spartans got another vote, if in the morning someone other than the Gaians is highest then I'll write up some more optional rules for them, otherwise I'll start the game using whatever of these optional rules are most popular.