I've made a list of moves that would be candidates for dual types some years ago, to see if there is potential for this or if it was just gimmicky.
-Muddy Water: Water/Ground
-Scald: Water/Fire
-Octazooka: Water/Poison
-Shell Blade: Water/Fighting
-Water Pulse: Water/Psychic
-Crab Hammer: Water/Dark
-Heat Stamp, Fire Punch, Blaze Kick: Fire/Fighting
-Fire Fang: Fire/Dark
-Flame Charge: Fire/Electric
-Heat Wave, Fire Spin: Fire/Flying
-Fiery Dance: Fire/Bug
-V-Create: Fire/Psychic
-Inferno: Fire/Ghost
-Thunder Punch: Electric/Fighting
-Electroweb: Electric/Bug
-Thunder Fang: Electric/Dark
-Ice Fang: Ice/Dark
-Avalanche: Ice/Rock
-Ice Burn: Ice/Fire
-Freeze Shock: Ice/Electric
-Ice Punch: Ice/Fighting
-Icy Wind, Blizzard: Ice/Flying
-Mud Bomb: Ground/Water
-Ground/Fire: Earth Power
-Drill Run: Ground/Steel
-Bone Club, Bonemerang, Bone Rush: Ground/Dark
-Absorb, Mega Drain, Giga Drain: Grass/Poison
-Leaf Blade, Wood Hammer: Grass/Fighting
-Needle Arm: Grass/Dark
-Solar Beam: Grass/Fire
-Leaf Tornado, Leaf Storm: Grass/Flying
-Psycho Cut: Psychic/Fighting
-Dream Eater: Psychic/Ghost
-Sky Uppercut: Fighting/Flying
-Sludge Wave, Acid Spray, Acid: Poison/Water
-Poison Jab: Poison/Fighting
-Poison Fang: Poison/Dark
-Razor Wind, Brave Bird, Drill Peck: Normal/Flying
-Mega Kick, Mega Punch, Thrash, Dizzy Punch: Normal/Fighting
-Fake Out, Hyper Fang: Normal/Dark
-Sky Attack: Flying/Fire
-Hurricane: Flying/Water
-Acrobatics: Flying/Fighting
-Dragonbreath, Outrage: Dragon/Fire
-Dragon Pulse: Dragon/Psychic
-Twister: Dragon/Flying
-Pin Missile, Twin-needle, Leech-Life: Bug/Poison
-X-scissor: Bug/Steel
-Bug Bite: Bug/Dark
-Silver Wind: Bug/Flying
-Signal Beam: Bug/Electric
-Ancient Power: Rock/Ghost
-Stone Edge: Rock/Dark
-Shadow Punch: Ghost/Fighting
-Shadow Claw: Ghost/Dark
-Hex: Ghost/Poison
-Bullet Punch, Meteor Mash: Steel/Fighting
-Mirror Shot, Flash Cannon: Steel/Ice
-Magnet Bomb, Gyro Ball: Steel/Electric
-Steel Wing: Steel/Flying
Thats taking it a bit too far perhaps LOLOLOL
but if they were to introduce dual types...it would be wtf to not change at least some of these, that just make sense, like Muddy Water, Earth Power, elemental punches etc.