First, I really like the idea. I have this old cliché western opener in my head, where the map burns away from the inside to reveal the first scene. Maybe the map changes in a similar way, burning away parts to replace them with new ones, depending on what the characters want or need.
Second, I think it really depends on what you want to do with the map. At first glance, it sounds like a plot device, and if you don't want to restrict yourself too much, just leave it at that. You can declare things on it if you want to force the players somewhere, and the players can declare things on it to help them out of trouble.
On the other hand, you could make the map an item of power on a "group character". You make a virtual character that represents the whole group of characters. Everything they have as a group is represented in that character. The map would be an item of power with worldwalking, probably. Maybe some minor powers to do with divination and such as well.
You might want to think about who created the map, and why. Was it an attempt to make a map of entrances to the nevernever? A way to keep track of the biggest nasties, so the wardens in the new world were able to hunt them down? Was the map created to be one thing only or to be adaptable to the needs of whoever holds it? Maybe there are additional items that can unlock different functions of the map, like special lenses you have to look through, and the map gives clues to where to find or how to create those lenses. Or the map might alter their ways through the nevernever to draw them to one of those lenses, in order to give them access to a place they need to be. Maybe there is a bob-like spirit bound to it, only it can't communicate directly with the owner of the map.
Sorry for the disorder, once my mind goes into brainstorming mode, it is hard to keep track.
Hope there is something in there you can use.