Hybrid PoW/PoS for Monero would help fighting the fractional reserve practice from shady exchanges. Either they will offer XMR staking and won’t be able to fake it as rewards will accrue over time and would become a liability for exchanges that aren’t actually staking XMR or a large share of their users will move their XMR to a service that offers staking rewards (or they will do it themselves) which would put pressure on their real reserves.