You know, as realized as Herbert’s Dune Universe is, it is in areas like this that I wish we had an even deeper understanding of the broader context of the Imperium’s government.
Clearly, that was all completely wiped away in the very first book so would have been somewhat wasted and later books make even more radical time jumps so hard to world build across thousands of years.
I do also realize the absurdity of complaining that we don’t have more information for imaginative games, i.e. isn’t this an opportunity to craft your own small addition to Herbert’s lore? I guess it’s an acknowledgement that I’m not sure I trust myself to meet Frank’s high standard.
More on point, I think I’ll take a look at the Holy Roman Empire and its system of Electors. I want to say they would meet in conclave for certain decisions (not least of course, was for the election of a new Holy Roman Emperor). For some reason Aachen or Cologne sticks out as a more or less permanent meeting place (this probably changed over time) although I could completely wrong about that.