For your CPU only idea,your best best is Scrypt even though it's been shown to be possible to mine on a GPU (maybe there's a CPU version of it,I just don't know)
As for your Nvidia only coin idea-you'll need to make your miners require CUDA (Nvidia only,can't run on Radeons) rather than use OpenCL (both Nvidia and Radeons) for the CUDA only coin.
After you sort out these two obstacles,you need to be able to show the merits of your idea so that a wider audience will be convinced that your ideas have merit rather than some experiment that'll be shortlived (like SLC,Tenebrix,Ixcoin,etc).Your ideas also need to be something that people will be happy to actually use to trade for things.Making coins for the sake of mining won't exactly be valuable (due to limited uses).
I'd like to see how this develops