Dorey
Riddle
Jossi
Kalle
Hayward
Solberg
Kempainnen
Rolland
Bertoni
and depending on how their rehab goes...
Vanular
Phillipi
Any one of those names could be a threat for next year.
Tanner is unbelievable, but not unbeatable.  He generally wins the comp by outshining everyone in training, and then the judges put him into an untouchable score category, so he simply has to land a run to win.  There are a lot of guys on that list who go as big, have as much style, and are just as tech (or more so).  Tanner has the consistency and the persona that simply makes everyone think that he is the one to beat, but his pipe run is well within reach for some of these up and comers.
Dumont has been getting beat by some of those guys already this year (48 straight, World Superpipe Champs), so you know he is within reach too.