Because it's late and I can't sleep and feel like collecting statistics instead... Here are some stats on Dojo updates.
Mario: 7 updates, most recent 8-24 (boss: Petey Piranha)
Legend of Zelda: 6 updates, most recent 8-20 (moves: Link)
Kid Icarus: 5 updates, most recent 8-9 (final smash: Pit)
Yoshi series: 4 updates, most recent 8-23 (final smash: Yoshi)
Pokemon: 7 updates if counting Pokemon Change, most recent 8-13 (Pokemon Trainer profile and Pokemon Change)
Kirby: 3 updates, most recent 8-27 (item: Superspicy Curry)
Star Fox: 4 updates, most recent 7-16 (music: Space Armada)
Metroid: 4 updates, most recent 7-19 (profile: Zero Suit Samus)
Wario: 2 updates, most recent 6-29 (moves: Wario)
F-Zero: 1 update, most recent 7-2 (assist trophy: Samurai Goroh)
Donkey Kong: 4 updates, most recent 8-22 (profile: Diddy Kong)
Animal Crossing: 3 updates, most recent 8-23 (music: Go K.K. Rider!)
Fire Emblem: 3 updates, most recent 8-7 (moves: Ike)
Mother: 1 update, most recent 8-10 (item: Franklin Badge)
This is why I'll tend to assume Star Fox, Wario, F-Zero, or Mother updates in the future.
Other stats:
Items - 9 updates, most recent 8-27 (Superspicy Curry)
Bosses - 1 update, most recent 8-24 (Petey Piranha)
Final smashes - 7 updates, most recent 8-23 (Yoshi's)
Music - 7 updates, most recent 8-23 (Animal Crossing: Go K.K. Rider!)
Character profiles - 16 updates, most recent 8-22 (Diddy Kong)
Story mode updates (non-bosses) - 3 updates, most recent 8-21 (Subspace Army)
Moves - 4 updates, most recent 8-20 (Link's)
Techniques - 6 updates, most recent 8-16 (Tether Recovery)
Game mode updates (non-story mode) - 3 updates, most recent 8-15 (Stickers)
Assist trophies - 5 updates, most recent 8-14 (Devil)
Stages - 9 updates, most recent 8-2 (Castle Siege)
This is a more interesting blend, and I'm not sure I should predict anything from it other than a stage, because it's been a really stupidly long time. If anything, it might be that the types of updates Sakurai's put up most often should be expected most... More items, final smashes, music, character profiles, and stages in the future seem like safer bets to me than the other types.
Also, out of the four series I listed above that I think are most likely, Star Fox already has music, a character profile, and a stage. So I'll be sticking with predictions of Wario, F-Zero, and Mother stuff for now. >_>