I'd love to see a clarinet with more of the characteristic dark, woody quality in the clarion register (C above middle C up to high C). The current one is great in the lower register, but not as "clarinet-y" as it might be up higher. A real German clarinet would be fantastic--a bigger, creamier sound than the French clarinets we usually hear. After all, it's hardly fair to have 3 oboes and only one clarinet.
Aggressive solo violins and woodwinds would also be great. And just for kicks, how about a whiplash (as in "Sleigh Ride") and sandpaper (as in the Nutcracker) in the perc. toys?