Nothing, it's already supported. In fact, Circom, one zk programming language, will output a Solidity verifier that can be deployed on any EVM chain. The proof generation would be run off chain, but the verification can and does occur directly on mainnet.

It already has zkrollups, which run zkapps off-chain but store their state and the proofs on chain. That multiplies Ethereum's transaction capacity by an order of magnitude or two, without losing any security.

Long-term, Ethereum might implement it natively, but right now the tech is advancing so fast that they're happy having multiple layer-2 systems doing it.