In short: PoS migration of Ethereum is in progress and will happen in stages. "Stage 0", which doesn't have any practical effects for smart contracts, is expected Soon (tm) (a few months probably).
It'll most likely be a couple of years until the transition is done so that smart contracts like Urbit can/will run under PoS.
Ethereum has been moving to PoS soon for a couple years.
It's still the intent, but PoS is effectively still unsolved. It's not just "can it decide blocks", it needs to have the right balance of incentives to be self-sustaining, or it destroys itself.
What makes you say that PoS is "unsolved " ? Did you hear about Cosmos for example ? Their mainnet is running for more than one year without any issue.
