As Stellar pointed out, Regional Variants do not need to follow in their original forms footsteps. Sandshrew and Vulpix family changed to Ice-types which is an opposing element of their original typing and the Grimer family went from being foul-smelling polluters to odorless garbage cleaners. It all depends on how they decided the environment affects the Pokemon that it will cause a change. Using my as examples:Don't hibiscus smell nice? It'd be odd to make an Alolan Vileplume into that considering it's based off of a flower that's infamous for smelling horrible.
Gloom/Vileplume/Bellossom: The abundance of sweeter smelling flowers, who's pollen and nectar they absorb, have caused Gloom and Vileplume to smell nicer and use their scent to calm and dull potential threats. Bellossom could instead be more night/moon active; during the day the Alolan Sun is so bright it's either in danger of burning/prefers to stay inactive to absorb as much sunlight/will turn its sweet fragrance to a more sour smell while at night the Alolan Moon is as bright as the sun is in other regions so dances and releases sweet fragrances then.
Farfetch'd: Leeks aren't a native grown Alolan plant so they substituted with something that was equally as long or longer: core of palm trees.
Koffing/Weezing: Absorbing the massive amount of gaseous releases of Alolan's active volcanoes have changes what chemicals it stores.
Jynx: Having observed how natives Alolans use dances to communicate messages and feelings, Alolan Jynx have put more focus on their dancing.
Xatu: Draws upon ancient Alolan ritual and ceremony masks to see different visions depending on the mask it wears. While wearing the mask its brought to a frenzy, as if possessed by the mask.
Sunflora: The Alolan Sun has caused its head to grow bigger, it body growing bigger and more studeir to support the additional weight.
Pineco/Forretress//Shuckle: To better disguise itself, it has changed its shell to resemble a native Alolan nut.
Think they should save a possibly Rapidash Pegasus regional variant for a Greek/Italy/Arabian-based region. Same with Mr. Mime, except with a English/Germanic-based region where the tales of the Fair Folk are from. I also feel anything they could have done with Kingler and Noctowl was done with the Crabrawler and Rowlet family.
Also try to ignore exact changes you'd like to see done. Already we're skipping on the edge of Smogon's rule of wishlisting, talking about cosmetic and flavor text changes we'd like to see done is alright though talking about specific Type, Ability, and Stat changes might be crossing the line. Of course if I'm wrong than Mods cross out this last paragraph.