Not all RDP clients support sharing all types of local resources. The MS desktop RDP client included with Windows does, and pretty much always has.
The Windows Store app in question is not the same client program, so there's no guarantee it will support the full RDP protocol. They may add those features at some point, but that's speculation.
As Jens Ehrich points out in his answer, the Windows 8 desktop RDP client (v6.x) still fully supports all previous features, plus all the new ones in RDP version 8.
Additionally, all Windows Store apps are highly limited as to what parts of the File System they can access, which could greatly hamper what you are attempting to accomplish. :)