"As an API Developer, I want to support a global rate limit regardless of whether my API is implemented within MediaWiki or in a microservice, so that I can use the best tool for my job."
Optional, since the first API mounted (MW REST) is built inside MediaWiki. It's likely that microservice-based APIs will be coming soon. At the very least, we should not prevent this user story from coming later. Note that this doesn't have to be transparent to the API Developer; it could be handled in the service (or in service-runner framework).