One of the best features for the update would be a scalable interface like the new SD3. Actually, just copy the entire SD3 interface and make it into an EZ-styled one. Done and done!
Some trickle-down features in a more simplified version from SD3 would be great. Like a trimmed down selection of effects to be able to give more control over shaping the sound. Even just a couple different reverbs, compressors, and a transient shaper could go a long way in tweaking the sounds. I realize that EZD is supposed to be "plug and play," but some expanded sound shaping abilities over EZD2 would be a welcome addition.
Also, +1 for the MIDI editor and time signature change features. The time signature change feature would be my favorite of these two features, as it would make utilizing EZD for live performances a much more attractive option.