I'm gonna operate under Mario Kart DS rules for this since I like how that game handled it. Here's some rough ideas:
SYRUP
Standard - Teacup (Ship modelled after the S.S. Teacup and WL2 machines)
Unlock - Turbobo (Vehicle in likeness of Bobo)
RUDY
Standard - Bulldog (Wario's biplane from WL3 and VBWL)
Unlock - Merry-Go (Based from WL3's music boxes)
SHOKORA
Standard - Sound Blast (Design sense from top-row Item Shop weapons in WL4 and the Sound Room)
Unlock - Diva (Modelled from golden treasures stowed in the chests, perhaps the rocket)
Watch me scribble designs for these sooner or later. It'll probably happen.