Protoshares and Memorycoin(2) run very memory intensive hash algorithms for every cpu thread running on the wallet qt miner it was suggested to have 1 gb RAM. I believe the OP is looking for something that would be mineable for an average computer that could not be taken advantage of by botnets, and which would take a long time for a gpu miner to be created. Or be disadvantageous to run a gpu to mine.
(also i know asics memory is on die, im saying it would be a neat feature if a future scrypt n miner was able to put in better memory as needed)
I already proposed a Proof-of-Work that satisfies the above requirements, over 2 months ago.
It's called Cuckoo Cycle.
You can find a whitepaper and implementation at
https://github.com/tromp/cuckoo