Other than the London Hardfork, the next biggest upgrade in the history of Ethereum is expected in June 2022, as the network transitions to full proof-of-stake (PoS) consensus mechanism.
Originally, just like Bitcoin, Ethereum was just a Proof-of-Work (PoW) blockchain, but introduced a PoS Beacon Chain on December 1, 2020, with about 9,500,000 ETH ($37 billion, in current value) already staked there.
The merging of the Beacon chain and the main Ethereum chain is the next expected upgrade in June 2022.
According to Ethereum, Proof-of-Stake comes with a number of improvements to the Proof-of-Work system:
Better energy efficiency – you don’t need to use lots of energy mining blocks
Lower barriers to entry, reduced hardware requirements – you don’t need elite hardware to stand a chance of creating new blocks
Stronger immunity to centralization – Proof-of-Stake should lead to more nodes in the network
Stronger support for shard chains – a key upgrade in scaling the Ethereum network
With the efficiency expected from the merge, the network will cut down its issuance of Ether to validators, such that, altogether EIP-1559 and the Merge are expected to cause Ethereum to burn more tokens than issued.
This will eventually result to Ether becoming deflationary.