Were I playing (which I'm still in the gray area about) I'd like to be able to switch between 2 saber, single saber, and double bladed. Period. I doubt if they will give very much emphasis on the lightsaber forms aside these varints and I suppose that's fine, but I would want to be capable of utilizing each variant without severe penalties because switching around is a matter of pragmatism. Different situation requires different armament.
IRL it depends on the sword or swords you are using and the opponents you're facing. Darkkender is pretty much right, though, 2 blades or double ended weapons typically were more aggressive. But it depends what style you're using and what style your enemy is using. Larger blades I can say this is so.
In sabre & rapier fencing, though, 2 blades increases both your defense as well as your offense since you constantly have to switch between defense and offense anyways.
Miyamoto Musashi developed the 2 blade style of katana combat. He believed that while there were some maneuvers that required 2 hands to execute, you [otherwise] should not need to use 2 hands. Offensive and defensive. Obviously every weapon has its attributes, pros, and cons.
I don't know the mechanics of how games will be but I think the way it has been like in KOTOR 1 & 2 worked well enough: 2 blades increased both offense and defense (in some respects more than others), but it might perhaps leave you weak on the front of vs. force powers.