2 years ago Timo updated the mediawiki RCFeed configuration code to make parameterizing RCFeed implementations easier. He did this after EventBus hacked around the existing code to map 'eventbus://' URIs to the proper classes.
https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/330833/
I always meant to update EventBus to use this, but just never did. We need to do this now before T214446 is done, since that task will change the way EventBus is configured too.