The actual bidding process is obviously still years away, but there are at least 2 good reasons to start to make some noise about it already: First, to make sure that no other South American country applys for 2026 (Venezuela, possibly together with Colombia would be an option) and second to gather support within Argentina and Uruguay for some joint infrastructure and economic development projects.
Like Danny sais, I doubt Argentina is currently able to pull it off (and Uruguay will be a minor partner). So while there still is plenty of time, they'll need it to get their countries in shape enough, and having a decade of history of successfull joint projects with already improved road & rail connections to point at when it comes to bidding would certainly be a boon to get FIFA officials look friendly at a joint bid, so starting the project early does make sense to me.
As for stadiums/host cities, I'd do it roughly along those lines:
2 Montevideo (apart from the Centenario, the Gran Parque Central of Nacional could be upgraded/rebuild to around 40k seats without turning into a real white elefant)
1 somewhere else in Uruguay (it's going to be a white elefant, no matter what, so best done with many temporary seats)
2 in Buenos Aires
10 stadia in 8 locations, all reasonably sizable metropolitan areas except for the 3rd one in Uruguay. Not even including Mar del Plata or Salta I don't think the problem is finding host cities, at least not in Argentina, the problem will be finding the money to upgrade infrastructure and build stadiums to a level necessary for the World Cup.