

IMO, while a hybrid approach might be eventually necessary, I don’t see PoS as part of the solution. But there are viable solutions (see below).
The problem with Qubic is that a few players can (temporarily) disrupt the network. The tokenomics of Qubic allow it to attack temporarily but it will ultimately fail by that same tokenomics. With PoS, the problem is that a few players (the stakers) can disrupt the network. The requirements for staking (e.g. not turning off your machine for a set period of time, etc) encourage people to stake with a service so it encourages non-custody and centralization. And since PoS gives stakers more stake, their power to disrupt can only grow.
So you’re trying to fix one set of disruptors by adding a second set of disruptors. Not exactly a solution, IMO.
Of course there’s slashing. If it’s purely algorithmic slashing, then it can be gamed and taken advantage of by either disruptor. If it’s “trusted individuals” then you’re just adding another set of disruptors to the mix. With so much complexity and potential for collusion, it’s almost certain that failure will eventually result.
So what’s possible? There are other consensus mechanisms that greatly reduce block reorderings like GhostDag (see Kaspa) that might be used to support the current PoW. Nano also has no transaction fees and seems to keep working. Instant validation of mutually agreed upon transactions also work if both parties are online at the same time (it doesn’t work otherwise). If I give you cash, and you accept the cash and give me a receipt for that cash in real life, I don’t need a third party to validate it so it would be wrong for a third party to not confirm it on the blockchain as finalized. You can even add the condition of having both parties have a copy of the receipt and both parties have to sign it. That extra condition is usually a part of the transaction of big ticket items like houses for extra security. True this approach wouldn’t work if one party is offline, but since I estimate for over 90% of transactions both parties are online (since NFC cards aren’t common but phones and computers are), this approach would all the blockchain to keep working even if there is an attack. The other supports are there for offline transactions.
As explained many times PoS XMR is the surest way to permanently centralized Monero because of the Cantillon Effect and slashing. That being said, PoS time or effort (see Torrents) can work. Essentially, the more you devote your machine to validate, the cheaper your transaction fees are. That wallets would then be encouraged to add an “validate in the background” feature. There would be no slashing…you either validated and got the discount coupon on the next transaction or you did not. AFAIK, nodes are validated each time someone syncs the block chain. There is a lot of work being done that’s just thrown away because it’s not recorded. If that work were recorded, you could have a hundred validations in 2 minutes and finalize blocks far quicker.