While I think rooting will be possible I would say not about flashing same ROMS as other GS2. I think that would be a big mistake. If I am not mistaken this would likely result in a brick, because the other GS2's are GSM, which is a different radio and thus wouldn't work properly on the sprint version.
Same thing with the original GS, GSM to GSM would work a lot easier, but I believe developers still have to port things over for everything to work correctly.
I am almost positive though loading a custom ROM right now from one of the GSM GS2 will not be good, and likely require some kind of backup, probably an odin if that is what is still being used on Samsung phones.
Though I don't think it will take long for this phone to be rooting because of everything already out there for it, and I think custom ROMS will be almost as easy to do, so we should get plently. Cant wait for some CM7.