There is a "maximum concurrent requests" option in the Advanced section of the Geocoder parameters. But considering most of the services you can access through the Geocoder have rate limiting protocols in place I don't think it can be improved much.

I agree here. I just tried it with my own ArcGIS Enterprise locator service and it still took 42 minutes to geocode just 9000 records. Neither increasing resources on the GIS server or upping the Maximum Concurrent Requests in the transformer did anything. It would be REALLY nice to have a performant out of the box geocoding transformer to use as some of the python solutions are either way complicated or too finicky to rely upon.

@Steve Schunzel​ at the moment I don't believe we have any plans to create an out-of-the box solution. If this is something you're interested in and you think other users might find useful, I highly recommend creating an Idea in our Ideas page.

You could try splitting your data into multiple streams and passing it through multiple Geocoders, but performance will still be limited by the Geocoding service.