Yes, it can be done, but until there's anything more polished, you have to deal with screens. Both (or more) screens can be visible at the same time, they update automatically etc, but you have to swap screens to get mouse pointer to right screen.
I started to write program, which will change screen to correct one when moving mousepointer on the edge of the screen. It works pretty well, but would need some fine tuning. I made option that you can define left and right screens (for example ibrowse screen is always on right and wb on left) or if you won't define the screens, then it cycles them back and forth. It also places the pointer to other edge when moving to other screen, so it looks like you just drag it from the other to other.
But anyway, remember that there's option in both P96 and CGX that those won't blank the inactive screen. So all screens can be visible all the time. I've tried this with two Zorro gfx-cards at same time and with PCI + Zorro card too. And of course AGA can be the third display too
And I guess nothing stops you from adding more Zorro cards for example.
For curiosity, we've played dynAMIte with two displays. Other player used joystick and other keyboard. All in one A4000 with two Zorro gfx-cards. Two dynAMItes were started and configured to different displays. We also tried that one plays Payback with joystick, while other uses irc on other monitor. On one A1200, with Zorro gfx-card and TV on AGA. Worked fine.
