There are side scrolling games that are not platformers, like Elevator Action and Kungfu. Has anyone tried making a procedurally generated game with those as a model? I think Red Rogue is a bit like this.
The main problem I see with platformer level generation is it is the actual spacial layout that is important. A top down game can focus more on content of the rooms, it's not so important exactly where the rooms are in relation to everything else. Put in another way a plaformer level is interesting do largely to its architecture, while the same is not as true for a top down game.
So I think that's why we are't seeing a lot of good platformers, but we are seeing some good side scrollers.
Maybe?