As you may recall, I wrote about this two years ago. At the time, it seemed that Medium didn't want competition for its few Medium-operated or partnered-with-publications (https://medium.com/illumination/is-medium-a-malignant-narcissist-1f3d55793bf6). Now that the boost program has indicated a clear shift back to empowering member-owned and operated publications and Medium's reliance on their unpaid workers (https://medium.com/illumination/a-spiritual-bad-assess-assessment-of-ev-williams-announcement-c78379698509), they should increase the number of editors that a pub may utilize. They can base it upon the number of stories a pub on average publishes (assuming they don't want to tackle it from the other end, and back-door to an article limit if they feel a pub is too large--in other words, they could say manage your workload by publishing fewer articles per day).