Port it to a modern language so PHP can finally die, add support for PostgreSQL and MS SQL
> All of WordPress as a .NET Standard assembly, without PHP.
Mentions both performance and security benefits.
Those kind of changes are good for PHP, because they give you more tools to write compact, simple code that plays nicely with some of the legacy builtins/libraries and so on. It's remarkable how much it has been improving.
However, it's still a clunky language, because almost every feature has its weird caveats and limits that a more modern, well designed language just doesn't have.