Also, take into consideration that you can build stuff with sidechains. No consensus is required, and it is based on the Bitcoin blockchain.
I'm pretty sure that PoW is already useful in that it accomplishes what Nakamoto2008 described for it to do, but I am curious to know how a miner-less blockchain would look like in terms of participants.
Me too. What I'm confident about is that a mechanism with a real-world cost parameter missing comes with great disadvantages.
(Proof of Stake / ETH) or banks (XRP).
It's pretty much the same thing. Bankers already work as stakeholders.