Internal scandoublers as far as I know have to clip onto the Alice
chip. They are true RGB unlike external scandoublers but cost you on
portability (swapping between machine) and I think genlocking might be
affected.
I'm sure you can get video enablers for those Zorro 4 boards...
I heard Eyetech sell/sold a monitor switcher that could be swapped by
simply tapping F10. Great for BlizzardVision PPC owners.
With a PicassoIV you don't need this and don't want the hassle. It's
such a wonderful board, try to do it justice with a video slot!
:-D