So, the first Setting book following the current paradigm came in 2018, with Guildmasters Guide to Ravnica (subsequent Setting books, aside from Exandria by an outside team, have followed the same layout as Ravnica, and SCAG is somewhat different). in 2.5 years, we will have received 5 Setting books, 6 if we include Acquisitions Incorporated (which we probably should), as opposed to 1 in the prior 4 years of the Edition. We know that there are at least two more "Classic" settings that were being actively worked on as of a year ago, with more on the way. That means we are seeing an average of 2 Settings a year in recent history, maybe more. I don't forsee that slowing down: and to keep that up, they'll need more Settings pretty quick. Magic crossovers fit the bill nicely.