Vitalik proposes changing EVM to RISC-V, cites CKB

"This post proposes a radical idea for the future of the Ethereum execution layer, one that is equally as ambitious as the beam chain effort is for the consensus layer. It aims to greatly improve the efficiency of the Ethereum execution layer, resolving one of the primary scaling bottlenecks, and can also greatly improve the execution layer’s simplicity – in fact, it is perhaps the only way to do so.

The idea: replace the EVM with RISC-V as the virtual machine language that smart contracts are written in.

Important clarifications:

The concepts of accounts, cross-contract calls, storage, etc would stay exactly the same. These abstractions work fine and developers are used to them. Opcodes like SLOAD, SSTORE, BALANCE, CALL, etc, would become RISC-V syscalls. In such a world, smart contracts could be written in Rust, but I expect most developers would keep writing smart contracts in Solidity (or Vyper), which would adapt to add RISC-V as a backend. This is because smart contracts written in Rust are actually quite ugly, and Solidity and Vyper are much more readable. Potentially, devex would change very little and developers might barely notice the change at all. Old-style EVM contracts will continue to work and will be fully two-way interoperable with new-style RISC-V contracts. There are a couple ways to do this, which I will get into later in this post.

One precedent for this is the Nervos CKB VM, which is basically RISC-V."