Rolled marzipan as cake filling?
Probably someone has done this. Why not? 
On the other hand, you don't want a thick marzipan layer, because the material is expensive and has a strong taste, so it is more naturally to use the cream as the bulk filling and have a thin cover on top. This makes the cake more stable, too. If the cream serves as the frosting, it has to thicker.

Normally in a cake one often has the harder layer outside and the soft stuff inside.

As an inspiration, here is something that has marzipan on top of a jelly layer

http://en.wikipedia.org/wiki/Dominostein