It's hard to say what will happen next year. I hear rumours of an all-new zx-6r for next year, but to be honest, I've only heard that on chat rooms like this - not exactly the best places some times to pick up rumors. I also rode all the 600's (except the gixxer) and I would choose the 6R over the others. Here's MY lowdown (not exactly the gospel)
Honda - (F4, I never rode an F4i), Good all around bike, better for new riders than all the rest because the power is so linear. Good all-around bike. Bars seemed really high to me, decent seat (f4i's is a major step back there). Seemed like ya had to really rev it to make power. Handled really neutral, another reason I think it was a good beginner bike. Docile when ya want to, but able to run hard if ya want too. Decent 2 up, good fairing.
Yamaha - (01 champ edtn) Really weak brakes, this was a letdown. Biek is really small and light (good & bad). Nimble, but not quite as planted as others. And forget about 2 up. Didn't seem to want to make any power below 1000rpm's. Pulled well after that. No wind protection. Handles really well. Tranny is really clunky, and ya gotta really launch it right, not like the other 600's. Sound slike I'm dissin' it, I'm not, but I think it makes a much better track bike than a street bike. I almost got one, but found a deal on my 6r instead.
Kawi - Best usable power of the bunch, down-low and midrange is great. Nice sound even for stock can. Nice ergos, can do 2 up. Silky smooth tranny, brakes are much better than my old 99's were (even those were better than the r6's). Weighs only a bit more than the r6, but it feels heavier, but it's splanted and stable in corners and at high speeds. Good seat. Good wind protection. For me, it makes the best street 600. I still love the sytling, but I do with all the others too.
So for me, I think I'd still get a zx-6r regardless of the changes the others make next year. If not, I'd probably go with the honda. The R6 is out cause I take the wifey sometimes, and the gixxer, as sweet as it sounds seems like it's probably too track oriented too (but I don't know yet).
Anyway, I think maybe we'll see the 636 hit North America. In the UK, it's either the top selling sportbike, or the top selling 600 (I forget). Also, Superbike (UK mag) did a 600 comparo with all the Japanese 6's, TT600, & the Ducati 748. Well, the gixxer took top grade, but guess what they picked 2nd? The 636. And yes, this included track testing. They loved the chassis, motor, brakes, etc etc. So I don;t think it's going to be a valid statement to say the kawi won;t do well on the track anymore. Cause even if the 636 motor doesn;t arrive, you can probably bet the other changes (chassis/suspension etc) will be applied. Whew! Well I'm done.