Interesting that you mention this with the current competition going on...
I have thought about this idea before, when I was interested in game development. Platformers are a unique form of two-dimensional games focused on providing a straight-line path with height as the second axis, where overhead two dimensional games are focused on providing a world which you can explore by allowing the player to travel in four directions (but limiting the use of height in these worlds). As you mentioned, the problem with converting three dimensional games is either the height (in overhead view games) or the depth (in platformer games).
A unique way of solving this problem is by allowing a sense of depth in a platformer game by allowing a player to move towards or away from the screen. This idea is excellent in theory, but how well would it work in practice? There would always be a limitation of this feeling of depth that you can create, and therefore you would have to modify the world, dungeons, and every other aspect of the game to fit within these limitations. Not necessarily a bad thing, as I have seen in a two-dimensional platformer version of the island from Wind Waker. As you said, the world map is one of those places where this idea would not work very well. Another potential problem I can see is with the fighting. Since a platformer only allows you to face (and attack) in the two basic directions, how would you attack an enemy that is deeper into the screen than you with... say your bow and arrow. Would you have to move away from it, travel deeper, then shoot?
Perhaps it would be better to think of a better way to incorporate height into the traditional overhead view...
