I begin by apologizing for my lack of knowledge and expertize on the field…
However, I wonder, why not piggyback PoS on PoW, and rely on sha256 Miners to validate value & Ownership, and PoS to handle smart contract by warping onto said block and adding to the block-chain.
I think SHA256 is the reason Bitcoin had surged in value, therefore Ethereum on SHA256 would have no problem scaling up with the transaction speeds !!!
In my opinion, assic miners are the only hashing power that can scale up the transaction speeds, and the more hashing, the more electrical power… If you want to go green, make miners use solar energy or Hydrogen generators.
In my mind, PoS could also work as a title company that, examines the title prior policy, checks against Liens/claims, clears title/validate, issues new Title policy, and logs history of all prior title policies/certificates.
Also, figure a way to have all mined coins to be cashed only by the consensus of the coin holders, in a manner that preserves the exchange value of said coin, preferably yields an appreciation of value to said coin itself, by retaining market Cap & reducing circulation… And most important, offering miners a very profitable and rewarding 50 or min of 25 coins per block in a continual bases into perpetuity.