This has existed (at scale, not just experimental prototypes) for over 10 years. I can't recommend anything in particular as I don't use it myself, but the very

This has existed (at scale, not just experimental prototypes) for over 10 years. I can't recommend anything in particular as I don't use it myself, but the very first search term I tried ("online jamming") turned up some useful leads. Direct integration with DAWs seems quite easy to set up nowadays.