Unfortunately, we live in a day and age where multiple monitors isn't very uncommon... I actually have a single (older, smaller) LCD that i dedicate to emulation in general...
No single SNES emulator can boast for multiple monitor support, and seeing as ZSNES has always been the best (IMO) I think that it should be the first one to grab my secondary display.
I do realize however, this is a very steep feature request, it requires a large re-write of the display code (or potentially just adding a secondary function and a couple variables)
Thanks for hearing me out, and keep up the great work guys.