But don't a lot of skills says "requires double bladed lightsaber?"
Fewer than you might think, but they're pretty fundamental: Force Breach and Shadow Strike both require DBLS (activating your different Techniques does as well, but you'll stay in it after you activate it; you only really need the DBLS when you're changing stances and can just get rid of it otherwise). The spec least affected by the loss of the DBLS would be tank spec since tanks shouldn't be using Shadow Strike *ever* and Force Breach is the weakest of your attacks. The only major loss would be not getting the 5% accuracy debuff. Balance and Infiltration, on the other hand, would be pretty well screwed by the lack of Force Breach and Shadow Strike.