I dont like to see so much countries making one World Cup, but also i dont like when the selected country is a non footb all one, or a non so good country to explore/travel. The last one on Qatar was an clear example, the World CUp was made in a very tiny country with not football tradition , and only backed by the power of money.
With the increase on the number of teams I do not think FIFA has too much of a choice, the amount of money needed to organize the tournament has gone up while the logistic issues have scaled up as well, so it seems to me that the right decision was to let more than one country to host the world cup, what it must never happen again is to allow a country or a group of countries to buy the world cup, which is exactly what Qatar and probably Russia did before.
That doesn't matter by increasing the number of countries hosting the World Cup or countries being able to do it together, but there shouldn't be more than two countries because it will affect the number of countries that have the opportunity to qualify, because the host country will get automatic participation in the world cup later. If there are only two organizers, it will be easier to divide the portion of the matches for each country, each will get the same number of matches, one as the opening and the other as the closing, but FIFA always has an excuse because they are the organization with the power to regulate this, but if the 2030 World Cup organizers are won by 4 countries from the Americas how unpleasant that would be because it reduces the chances of other countries in CONMEBOL qualifying for the World Cup.
Four countries as a World Cup host will be too much because that would be very unfair to the other teams who will have to qualify and have a hard time to go through the qualifiers of which 32 teams will be only accepted. I think 3 countries will be the maximum line, although there's no written rule for this, it will be a common sense not to have more than 3 hosts to remain fair.
It's just that Canada-America-Mexico agreed to make a bid together to increase their chances and indeed, they succeeded and they are the first ones who will host the world cup with 3 hosting countries.