I'm in the same boat. I bought BF3 limited edition (came with Strike at Karkand) because they hadn't yet announced Premium. I think at that time the DLC wasn't a pre-order bonus, but rather an included perk to buying the limited edition. It's been awhile though so I could be wrong.
I'm not sure when China Rising comes out but chances are Premium will have been on sale before it does. I don't think they've announced the release for the China Rising yet. Someone correct me if I'm wrong.
December is what I've read. Which is on par with BF3.