If you use VSCode you can get that today, if you use something else it doesn't look too hard to write: https://semgrep.dev/docs/integrations/#editor

I'd expect latency might be juuust in the range where it doesn't feel interactive yet? But honestly any search that isn't ripgrep or --omg-optimized-etags feels like that to me now, and people use symbol rename features in IDEs all the time that take multiple seconds, so maybe I'm just unreasonably picky.

I created a semgrep rule for this: https://semgrep.dev/s/GRD6/?version=develop

This is actually a great idea.