Andrew, it’s 6* Regionals. The only case where there would be a 4th Champion would be the rare case where the Champion pulls in a backup team. That happens maybe once or twice per year, and can easily be covered by duplication elsewhere, or a Champion not being able to go (which happens more than you might think).
6* Regionals + 15 + 7 + 3 +1 - overlap +18 (the MI contingent)
For overlap, we’ll assume none, other than 2 Legacy teams also being HOF. (I think that’s the right number…)
Assuming that the number of regionals (not counting districts and not counting MSC as a regional) remains the same for next year, that’s 42 pre-qualifiers/MI teams + 6*43 regionals = 300 slots, minimum, with only previously known overlap. Currently, the Championship is running about 340 teams.
Given that 1-2 new regionals are typically added per year, and the number of HOF teams goes up by one per year, (so the team count goes up by 13 per year), I give it 4 years before the minimum has to be the current size, or the qualification system gets tweaked again.
Second assumption: about 30-40 teams manage to get doubly qualified every year, either through multiple event wins or through EI/RAS/RCA combined with an event win. (Or through special circumstances.) That’s another 30-40 slots available. 8 years before there’s a tweak, maximum, assuming constant growth rate.
More small regionals means either bigger championship, or more districting systems popping up sending X teams apiece.
Fewer big regionals means smaller championship, or more open registration slots. However, a number of regionals are already crowded. So you almost have to add more… which adds to the more regional question.
Either way, I predict that inside of a decade, open registration for the Championship will be extremely limited unless there is some major change to the qualification system. I suspect that that change will be similar to MI’s district system, when it comes.