The closest parallel I can think of would be the first Dawn of War series and all those expansions being standalone. You could only play the races of the expansions you owned in multiplayer.
right, i thought of that too. still, if you want Rebellion, theres no harm in pre-ordering that. In the worst case scenario, its just like if you went and got one of those dawn of war expansions. you have the new factions, but not the original. you can do multiplayer and whatnot. But what I was saying was that word about how it all will work isnt available now, if he wants to know so he can preorder
Im going to go ahead and assume that he wants to preorder now so that he maybe gets in on the beta. So, lets say he does that and then between now and then we get a message from the developers saying "if you have the original sins, it unlocks giant bazooka ships". So then he knows he has to have trinity to get that. If he really wants it, he goes and buys trinity and its still at least 3 days from release, so he'll be fine on day 1. where is the issue? if you dont think it'd be worth the money, im sure you would be able to cancel the preorder. seeing as how you dont even own anything.
and actually, the way I at least understand it: theres only 2 factons, rebel/loyalist, which are brand new and are breakdowns of the existing 3 races. so, not 5 anyway you slice it. Either 2 or 6.