I would assume at this point in the whole mario numbering cycle it would make more sense to stick with the NEW SUPER MARIO BROS label (considering each game in the nsmb series has sold what? 25 million each or so) regardless of which mario game was actually the REAL sequel to which game...
Therefore, even if they made a new game which was considered (by pedantic people) a direct spiritual successor to either smb 3 or smb 4, it would most probably be given a 'NEW SUPER MARIO BROS' tag such as NEW SUPER MARIO wii U or 3ds or whatever to risk confusing newer fans.
(To think, back when Mario 64 came out I was dumb enough to consider THAT the sequel to Marioworld...fortunately nowadays people are better informed! We were dumber back then in '96-97 and few people had this int-ren net thingy that's all the rage now so it was hard to keep on top of things)







