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I haven't seen any ideas from Arma that could become a key element for him.
To organize such a tournament, you need to rely primarily on the team captains, who will positively evaluate the idea and want to participate. And the captains will then assemble the teams.
That is, you need to survey key Heroes of Might and Magic players from different countries/regions.
Poland - Dawidu and Jelen.
Hungary - Dave_HUN.
Romania - Gee.
China - if herolwy doesn't start getting upset, then gather materials from many years ago and find contacts there.
Belarus, Ukraine - they will definitely gather, just contact a few of them.
And do we have a community in Kazakhstan?
Regarding the Russian regions, read who responds positively, figure out where they live, and talk to them about their willingness to stream (but thinking for themselves and critically evaluating what is said).
The regions are not the primary focus, but rather specific people living in those regions who will enthusiastically embrace the idea. It's not necessary to gather everyone at once; it's enough to have those who want to participate. And once it works out the first time, the others will want to join the second time.
In my opinion, it's not necessary to gather 16 teams.
Even if there are 8/12 teams of 4 people each, with the possibility of one substitute, that is, 3 players (the simpler, the more reliable), and if there are captains who support the idea, it will still be an event unlike any other. And as a first step after a long period of inactivity, it will be significant.