Miyamoto doesnt have a good idea for it, so wont include it

Many of the launch Nintendo 3DS games havent included any form of StreetPass functionality. Others, though, like Super Street Fighter IV 3D Edition, have included some very comprehensive StreetPass features.

The upcoming Super Mario for Nintendo 3DS (which doesnt even have a final name) will be one of those games that doesnt have any StreetPass functionality. Not because Nintendo or Miyamoto are lazy but because they simply dont have a good use for it.

Speaking to The Telegraph, Shigeru Miyamoto has that Super Mario 3D wont have the much loved SteetPass functionality "Unless a spectacular idea comes to mind". The game however will have some sort of gyroscope enabled camera control. However this will work wasnt elaborated on in the interview. Guess well be waiting for E3 then.

Source: The Telegraph