OK lots of things here to say. Incoming nerd essay...
By allowing bhop with a % speed cap as in tfc it would allow for a faster, higher skilled game but would not change the meta of tf2 IMO. a bhopping heavy to mid is still not as fast as a bhopping scout to mid and further if it followed TFC mechanics, the heavy can't shoot while bunnyhopping so he will still be largely a sitting duck once he starts spinning or shooting his AC.
A lot of people didn't like TF2 when it came out simply because it didn't have bhop anymore. Slowly, the game added advanced movement through different weapons like the boston basher and FAN. I always had a dream that once TF2 got big enough there would be a pro-mode or dedicated servers to running a bhop version of TF2 without a glitchy plugin. However, I think its clear this isn't going to happen from Valve's side. TF2 and CSS both have remnants of bhop/strafe jumping mechanics but the speed limitations in both games make it not advantageous to try to bhop. Along with the removal of grenades it is clear that TF2 is supposed to be a "cleaner more newbie friendly TFC". If someone could make a good bhop server for TF2 then I'd love to fill it with people and try it out but so far I have not found any of these servers to be good enough.
Long version short: TF2 gameplay wouldn't be hugely affected if it added bhop, but TF2 isn't "supposed" to have bhop so people would not accept it. For this reason, I am still holding out that TF3 will have concs and bunnyhopping hurrah!