I think we should welcome all efforts to have a standardized, modern select component in the HTML spec. Would save a lot of trouble.

We have one and have had one for years. It uses the OS's default design, which is familiar to users. Instead, we have had decades of people hacking together whatever is the trend of the day into a custom designed select-box, often providing poor accessibility and usability. The absolute worst offender of these has to be on mobile where iOS has its native control and many designs implement custom select's which don't trigger that.