Obviously there are many challenges in this approach as you could take a powerful rig, start x number of miners, and you have got round the problem.
The fundamental problem is around how we mine with solo mining, pool mining and P2P mining.
This means there is no way of implementing a diminishing returns algorithm without impacting everyone.
As per the OP the whole point of this coin so that GPU's cannot mine this coin. At the moment there are no new CPU only coins so this coins has a good opportunity.
Problem with the GPU Miner is GMP... Its not so easy implementing this as it is for other sph lib based algos.
But time will come