Some of those lessons have most definitely been used to improve the reference implementation.

It's not remarkably slow as long as you compare apples to apples, that is non-jitted vm-interpreters.

Jits pay a steep complexity- (and hence maintenance) price for their performance that should be taken into account when comparing.

Designing a significantly faster interpreter with comparable features is non-trivial from my experience [0].

https://gitlab.com/sifoo/snigl