Omar, with the pent-up demand and overall streaming numbers close to Oasis, The Smiths would undoubtedly sell out stadiums including in the United States. The band last did a full live show on December 12, 1986. That's forty years of waiting for their fans.
Morrissey attempted to recently give-in (after decades of offers and pressure) and book a tour of him and Johnny Marr as The Smiths but Marr has outright refused to ever make that happen going forward. Meanwhile, Morrissey is at peak demand as a live act, possibly ever, thanks to The Smiths' streaming surge.
What I think is likes of Arctic Monkey and Tame Impala, their audience definitely is different than audiences from "mainstream pop stars" like Taylor Swift, Kanye West, Adele...
If Smiths make reunion, they will definitely become arena touring act in America... Not sure if they will reach stadium level in US