BTW, What Rider Arts do we already know about?
Also, shall we speculate about those we don't know? Just to shake this topic a bit.
Like, do you think W will get Maximum Drives for all his forms as arts or something?
Let me see what I can remember...
[HIDE]-Kuuga Mighty Form: Mighty Kick
-Kuuga Pegasus Form: Shoots while dashing back
-Kuuga Ultimate Form: Pyrokinesis
-Agito Shining Form: Shining Clash
-Ryuki: Sword Vent combo
-Ryuki Survive: Meteor Bullet
-Faiz: Crimson Smash
-Faiz Blaster Form: Photon Breaker
-Blade: Lightning Sonic
-Blade King Form: Royal Straight Flush (Missing Ace ver.)
-Chalice: Shoots while dashing back.
-Hibiki Armed: Kishin Kakusei (shockwave ver.)
-Kabuto: Clock Up + Avalanche Slash
-Kabuto Hyper Form: Maximum Hyper Cyclone
-KickHopper: Rider Kick
-Den-O Sword Form: Extreme Slash (close range ver.)
-Den-O Axe Form: Sumo leg stomp.
-Den-O Gun Form: Shoots while dashing back.
-Den-O Super Climax Form: Huge jump (used before Super Boisterous Kick in the movie)
-Kiva: Darkness Moon Break (no night)
-Kiva Emperor: Final Zanvat Slash
-Decade Complete: Enhanced Dimension Kick (no cards ver.)
-Diend: Dimension Wall
-Double CycloneJoker: Wind-boosted continuous kick.
-Double Xtreme: Double Prism Xtreme
-Joker + Cyclone: Double Rider Kick (Joker has another, alone Rider Art)
-Accel Trial: Machine Gun Kick (no Maximum Drive, fast evade)
-Skull: Jump + aerial downwards shooting.
-OOO Latoratah: Revol Spin Kick
-OOO Tajadol: Aerial fire shooting/Magna Blaze?
-OOO Shauta: Liquifies.
-OOO Burakawani: Warning Ride
-OOO Putotyra: Aerial combo, finished by slamming the enemy against the ground
-Fourze: Gyro + Gatling (Note: has other Rider Arts)
-Fourze Magnet States: Shoots while dashing back.
-Fourze Cosmic States: Rocket + Elec, followed by Rocket + Freeze and then Fire Barizun Sword.
-Meteor/Meteor Storm: Entrance comet thing. Does not deal damage, instead lowers the Rider Gauge.
-Wizard Flame Style: Copy + Flame Shooting Strike
-Wizard Flame Dragon: Dragon Breath[/HIDE]
(note: Again, what I remember. I'm sure I'm missing some. As well, some might not even be Rider Arts, just looked like it in the PV.)
About speculation, I doubt Double will get all his Maximum Drives for Rider Arts (especially since CycloneJoker has shown something other than Joker Extreme, and LunaTrigger showed Trigger Full Burst as a normal attack). There's probably some of the moves that will be Rider Arts, but who knows which.