I've been reading lot of faq material and in it it was said starting area is about 10 hours long and of those 10 hours 7 is spend doing class specific quests. After that you get your ship and get to explore universe with every other class. I think it's safe to assume every area after starting area has a worse ratio of class specific quests than 70%. Why? Because it was your class' starting area after all.
Furthermore, it is a mmo. There are lot of people who want to play mmos with other people, with other classes, and want to be rewarded for it. In other words: their quest will go forward as they help a friend go forward. So I think it's safe to assume(yes again, sorry) class specific quests give only slightly different reason and/or different objective to go in a area full of enemies, but every class goes there. Basically, where jedi knight would go to kill the leader of sand people, smuggler would go to steal specific goods, but most of the time during their quests both of them would be killing sand people.
So, in practice, the 100 hours of class specific material would be actually a lot less.
I'm perfectly willing to be proven wrong by the beta people.