As I understand it, technically a ruling striking down prop 8 on equal protections grounds could simply force states that have civil unions to change to marriage, without forcing states not offering same-sex couple benefits to do so. Especially if it goes to SCOTUS and there is a favorable ruling in regards to same-sex marriage (which is questionable to begin with), this seems the most likely outcome since SCOTUS rulings tend to be as limited in scope as possible.