At CodeSandbox (https://codesandbox.io https://codesandbox.io) we're also working on this! Main focus of us is that we're running the environment in Firecracker

At CodeSandbox (https://codesandbox.io https://codesandbox.io) we're also working on this! Main focus of us is that we're running the environment in Firecracker microVMs, which allows us to snapshot and clone environments very quickly. This enables us to create a VM for every branch, which comes with the added advantage that every branch automatically has a snapshotted preview environment that can resume in ~2 seconds.