Too Long; Didn't Read
The main purpose of the upgrade is to make the blockchain FASTER (>15tx/sec) and more SECURE (51% attacks, centralization) This update will also imply a host of other changes, such as economic changes. The next phase is estimated to go live in 2021 and introduce shard chains. The mainnet will continue in the usual proof of work mode (validated by miners) until we reach Phase 1.5, so not anytime before late 2021. Once you’ve staked your ETH on the beacon chain you cannot withdraw it back.
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