There is no mining which is the big issue. The big issue with their plan is that they hold 85% of the outstanding coins, which at current rates makes them billionaires. No doubt they will liquidate it in chunks to move it from digital potential to cold hard cash.
PoS and MobileCoin validator nodes use about the same amount of electricity.
I'm not a fan of PoS because it looks like a ponzie scheme (unless it's done like eth where initial distribution is done via mining)
This is actually worse than PoS, because PoS uses standard public key cryptographic to validate ownership of coin in the chain to stake, it at least in theory can achieve "trustless" validation.
This on the other hand is just a shitty attempt to outsource database maintenance to untrusted 3rd parties, using SGX, while forcing them to pay for S3 hosting because they can't implement a DHT to do proper decentralized file transfers.
