It will be implemented when it's ready. There are no estimates from the developers yet, but I personally think it will happen sometime in 2018 or early 2019 at the latest.
It is already possible to do Lightning transactions on the Bitcoin testnet so it's reasonable to assume that we're not that far off from an official mainnet release.
I mean even if it is ready, this wouldn't mean that the rest of the people involved in Bitcoin (miners, exchanges, wallets etc) are going to want to actually implement this, as a lot of people have alterior motives and want