Proof of Stake is hardly uncharted waters, their is a large # of Proof of stake coins with different specs, that have been running for years.
(And all of them have a higher transaction capacity than BTC.)
And none of them have anywhere near the market cap, even though they have a higher transaction capacity, and they are not secure enough to have such a high cap. And there is emerging literature showing intrinsic problems with having proof of stake be long term successful and different proposals for solving it. It's not widely accepted that such a system can be valuable and secure long term.