>Wouldn't it just be Visual Studio then?

No, but it would "just be" an open source, MS backed, version of Sublime or TextMate. The concept of Visual Studio is different.

>We would get updates once a year instead of once a month.

The language the core is in is irrelevant as to whenever we would see updates. That's a concern of the release process.

>There are less C++ devs than JS devs.

Not really important, as most of the contributors are MS guys anyway. In fact a single person has made Sublime Text, an editor that offers most of what VSCode offers, with 1/100 the budget and manpower. If only it was Open Source too, or had a few more devs...