in 2026 I would assume that each group (of 3) will be based around one stadium, or if they go with groups of 4, 2 close-ish stadiums) to minimise travel time / logistic complications.
the expansion to 48 teams is madness. at least they are using (mainly) countries who have hosted before and have existing stadiums*
given that Chelsea fly to Leeds for club games, now sure that an extra 1000 miles or so for flights in the knockout stages matters that much.
*interestingly, the Azteca is the only stadium that will be used that previously hosted a world cup game.