I like the fast weapon switching as it is (i started playing with 2.3 so i never experienced the old way, but i've seen old demos and imo it's a definite improvement), but, like others, i hate the fast "nex to nex" switch.
I used to do it myself when i first discovered it (i even tried making a script for it but it never really worked

), but ashamed by my own lameness, i managed to kick the habit, only to discover later that most good players considered it a feature, not the exploit it clearly is

The way i act now is: i (try to) use it against players that use it, i (try to) avoid it with players that don't. Which is very confusing since it's all about muscle memory, and, more often than not, results in me fucking up my nex shots when i least need it
Also the fact that it's scriptable is beyond the point imo: sure, it make it even worse, but the resulting overpowering of the nex (like it wasn't overpowered already

) is good reason enough to make it impossible.
But, please, do as KadaverJack suggested and add a separate reload timer for the Nex, "proper" fast switching kicks ass and needs to stay as it is (hell, even faster!)