The last two DTs were very interesting and I think it is time we discuss this topic more seriously. There have been many posts about mutliplayer ideas, but now that the team is really working on it, we should gather ideas and thoughts so that the team has a rough idea what the community has in mind when they think about multiplayer.
Now on topic: The questions that arise are quite difficult to solve. When someone is hosting, this person will have serious performance issues, that get bigger and bigger the longer the savegame is played. More hearthlings and more structures and more enemies will bring down even the best systems out there and making it unplayable especially for the hosting person. So the question is, should team radiant limit the number of players?
I personally think: Yes! For me personally it would be enough to have a 2 or 3 player mode. Going higher then that can mean that there is not enough ressources for everyone and very soon the map would look like a switzer cheese. So 9 players is not needed in my opinion, 3 is enough.
But would this solution be good enough? There will still be plenty of people whos system is to weak. Therefore everyone should have the option to rent a dedicated server to run the game on. This way, the server had to host all the stuff, while the players can enjoy a good performance, since the dedicated servers will be standardized and will be strong enough to handle even 3 players with big cities.
Ofc. there are many things more to discuss, but the first questions we should answer (I think) is, how many players should be allowed and what kind of options the players have to host a game.