If the US did start adding 240v circuits they would almost certainly use NEMA 6-15 or 6-20 plugs for compatibility with (the rare) 240v appliances like air cond

If the US did start adding 240v circuits they would almost certainly use NEMA 6-15 or 6-20 plugs for compatibility with (the rare) 240v appliances like air conditioners or hotplates which use those plugs today.