Tying zoom to a modifier + scroll wheel sounds like a great idea. It’s a simple way to implement this that oughta feel pretty good.
I’ll do this before too long. I’m going to be literally rewriting the renderer as part of this mobile optimization work I’m on right now because I want to move Shmeppy’s rendering work onto users’ GPUs rather than their CPUs, and the GPU (essentially) speaks a different programming language than the CPU. This’ll affect how Shmeppy zooms. So I probably won’t try to bring in this change to zoom’s interface until after that.