I actually did to rewrite parts of django's auth, caching in go in order to be compatible with a grpc-based mobile app. The django source code is well documented and easy enough to understand, so it wasn't a probablem signing sessions, creating users etc in go and then using them in django.

For django itself, once I slapped a database caching layer on top and tuned gunicorn/uvicorn, there were no performance issues. Go is faster, but django is fast enough.

You don't need to do a full rewrite usually. Just pull one or two CPU intensive routes out into their own service.