The official estimate[0] is 2022. Given the general track record of their development pace, I'd be surprised if it goes fully live before 2023.
Re:Skynet – Build a Free Internet
by chrisco255 on Sunday January 10, 2021 @01:09PM
(#25717492)
It says shard chains ship in 2021. They are saying the ETH1 chain will be migrated to proof of stake in 2022.
See Vitalik's blog on rollups: https://vitalik.ca/general/2021/01/05/rollup.html