A desert board would be amazing. I would like it to be hard to get to. Either you have to enter through the Desert space in the Middle regions, somehow, or if you have the Flying Carpet you can get there, somehow.
One of the spaces I would like to see in a Forest or Woodlands board would be The Ancient Cemetary, which would have some similarities to the main board's Graveyard, but maybe more fearful. Like "Pet Semetary", maybe - if you take a dead animal/trophy there you can ressurect it, but there should be a danger element to yourself in the doing of that. Or the Ancient Cemetary can have a catcombs beneath it that may take you to other boards.
The concept of an ocean or sea would seem to be daunting, not that I'm against it. Sea monsters would be pretty much Dragons in water, so I don't see individual battles being impossible. But I want the scale of ships on the sea, so … ? The dynamics of sea voyage, in a fantasy setting may be challenging to sync with Talisman's normal sense of play. Does that make sense?