First of all, a big part of the reason why the M3 engine is more responsive to the throttle is the presence of individual throttle butterflies - the 335i only has 1. If you don't believe me, drive any other NA BMW with a single throttle butterfly and you'll see the engine response is not any better than the 335i - in other words, it's not necessarily a function of the presence or absence of forced induction.
I think some people here confuse turbo lag with engine throttle response. My observation was that the 335i definitely had turbo lag, but engine throttle response was very good. A 335i with individual throttles would have similar engine throttle response to the M3, there's no reason to think otherwise.
So about turbo lag... My chipped 335i had measurably more lag under 3500 RPM. But from around 4k-7k RPM it had practically no lag at all and as I've mentioned the engine response was very very good. Which is why for track driving the lag was never that big an issue as I had originally anticipated. You may question why have a torquey engine at all if you still have the rev it all the way, and there's certainly a point to be made there.
I as others here think that the M people can somehow mix together small turbos, DI, individual throttles, valvetronic, magic chicken feet and/or some stout Bavarian lager in a big cauldron and come up with a remarkable new engine for the next M3.