Minecraft already got a new engine, it was rebuilt from scratch in C++ for the "Bedrock" edition which powers all of the console and mobile versions, and is on PC alongside the original Java version. Unless you mean another new engine after that one, but in any case Notch's code was always a mess so he's probably not the man for that job.

I recall Java Minecraft modders having to optimize it themselves because the stock game was generating hundreds of megabytes of garbage collected heap objects every second, amongst other things.