Wildcard made a joke about "alien blood slaves" in a Dominions/SE4 crossover mod over at SE.net... hey, why not!
Although SE4 lacks "cultural influence" like Galciv has, dominion can be represented by the system combat modifier bonus given by stock war shrines; if you lose your dominion you won't die off immediately like in Dominions but you will be very easy to conquer, with the proper combat settings in Settings.txt
Ships would be your commanders; fighters would be your regular units. Priest ship hulls would give some sort of combat bonus (not sure how at the moment - SJ suggests storm abilities, but that would affect both sides); mages would be allowed to install powerful "spell" components; other "ships" would be limited to simple melee (short range DF) and missile (long range DF) weapons.
A system would represent a province, and planets would be cities and magic sites within that province. Per SJ's suggestion, systems could have a plenitude of random storms scattered about so that on occasion a magic site will be hidden!
Space Dominions
Threaded Mode