Hmmm...
I doubt they can fix SF such that we need not restart the game to get between SF and BF2-Vanilla. If that is really the case, putting in the grappling hook, zipline and some SF features required some irreconcilable changes to the game engine.
If the Booster Pack has no zipline, hook, and all, I think it'd be integratable with BF2-Vanilla... and therefore, you'd not be required to restart your game when you switch from a BF2-Vanilla to EuroForce, or the other way around.
And unlocked weapons 'd be available in all 3 versions.
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As I typed the above, I wondered: What if a server has a map cycle that has EuroForce and Vanilla maps? What if someone on the server did not buy the booster pack, and the next map is a EuroForce map? Probably then, the person 'd just be kicked, and a notification pops up to tell you that you don't have the required map.
Is there any server out there that cycles between Vanilla and SF maps? I guess when the transition comes... everyone will suddenly thrown out of the game... and the whole restart happens sans trailer n all. Is it possible at all?
My assumptions 'd be off if EA can actually integrate SF into vanilla, but did not, just to ease the process of seperating ppl with SF and ppl without (so as to avoid the map change issue). However, seeing the huge difference is lagging and loading time between vanilla and SF, I am betting on the former: that SF requires messing with the engine so much that we cannot just have one icon.