Basing it on RAM is even more foolish.

While most consumer grade hardware only supports ~16GB per system and the average computer has likely ~4GB there already exists specialized motherboards which support up to 16TB per system.  This would give commercial miner 4000x the hashing power of average node.  A commercial miner is always going to be able to pick the right hardware to maximize yield.  Limiting the hashing algorithm by RAM wouldn't change that.

BTW 2GB would be a poor choice as many GPU now have 2GB thus the entire solution set could fit in videoram and GDDR5 is many magnitudes faster than DDR3 (desktop ram). 

There is no need for everyone to be hashing.   As long as the nodes are sufficiently decentralized there is no need for them to be completely decentralized. 

Also it is unlikely you are going to achieve that level of decentralization anyways.  Currently hashing is worth ~$60,000 per day.  If you have 1000 nodes then the average node has a gross revenue of $6 per day.  With 100K nodes it is $0.06 per day. 

Given botnets have up to 230K zombie CPU to defeat botnets in numerical superiority you would need 230K+ nodes making average yield ~$0.02 per day before electrical costs.  Most people aren't going to hash for $0.02 per day and pay massive amounts of electrical costs.

This idea that wide acceptance of hashing is a requirement of wide acceptance of usage is flawed.  How many people run a VISA or Paypal processing node?  What is the ratio of end users to processors?

Sure we don't want a monopoly but as long as no entity achieves a critical mass we also don't need 200K+ nodes either.  If you are worried about the strength of the network a better change would be one which has a gradually decreasing efficiency as pool gets larger.  i.e. a non-linear relationship between hashing power and pool size.  This would cause pools to stabilize at a sweet spot that minimizes variance and minimizes the effect of non-linear hashing relationship.  Rather than deepbit having 50% and the next 10 pools having 45% and everyone else making up 5% you likely would see the top 20 pools having on average 4% of network capacity.

I am not saying we even need or should do that but that would attack the real problem not the flawed belief that GPU makes the network weaker. GPUs makes the network very botnet resistant.    Bitcoin likely would have been destroyed by botnets already (if out of spite or to simply see if they could) had it not been for the rise of specialized (i.e. GPU) mining.