Irae you are totally right about the weak number of participants in the last major and as you said the different themes are made so that it would be unlikely to have the same winner in several of these tournaments.
However even if I think there are not many active people around here, the community should be big enough to welcome more participants. Let us not forget that we managed to get 33 participants in Genesis (I know it is not that many but still), and we do not know how many more players we can gather because we are obviously more than that. There are some people who are just waiting for Arcade to come out, and others who do not play for other reasons, but maybe there will be more people who will show up if they are aware of this kind of event. Let us also not forget that seasons matter too since we are in the month of may. It means that students have probably finished their exams (there are not only students in our community, I am aware of this) and thus can have some free time (let us hope so).
HYNE I think your idea would interest many people in the community, so I think you should let everyone know about this in Discord today in order to have a quick feedback and have a general idea of the potential number of participants. The earlier it is done, the better.
As for the fifth tournament I would go for DC Ranked. It is always good to test something new and also... overdose of Official ruleset