Is there or will there likely to be any TV card support for classic? I mean by the Paloma module for picassoIV or any PCI TV card which works on mediator?
Dual boot is possible, all you have to do is install the two OSes on different partitions and have a way of choosing where to boot from. That might be as simple as going into the early startup menu and selecting the disk.
Someone could write a small program that would let you choose e.g. between OS 3, OS 4 and MorphOS. I don't see any trouble with that.