Very neat. I have embedded Javascript in Go before with goja and the results were pretty good. I used it to test Auth0 rules; they were in the critical path for our sign-in flow and a refactoring made some of them not work, so I just included them in the codebase and make sure they work against the API during the unit tests. I thought it was neat, and it made developing those rules much easier.
No doubt there is a lot of opportunity to do things like this, and using V8 probably gives you better fidelity against production (since they're likely running the rules with V8).