Sorry, I meant using a VDP2 3D plane (as in several 3d games, like Panzer Dragoon, Virtua Fighter 2, etc.).
Right now, I'm using the VDP1 for the ground, but I would need to add so many polygons to prevent the weird bugs (such as Sonic's feet disappearing).
It would also allow me to have an infinite ground floor, which would make something a bit like Sonic Utopia possible to a certain degree.
As for the slave CPU, I don't want to count too much on it for now as I still have a lot to learn first.