All eyes will be on Legends: Arceus' ambitious new direction, including its titular creatures themselves. The mainline series of games certainly needed a shot in the arm to shake up the formula, and the addition of Regional Forms and new/alternate evolutions have greatly spiced things up in addition to the latter games' new gameplay mechanics.
Scarlet and Violet will be ushering in the 9th generation of Pokémon, and it should make use of that in part by revitalizing some classic Kanto species. The likes of Eevee are no-brainers, but some underrepresented species deserve some attention too.
Machamp
Humanoid-themed Pokémon may have ittedly become played out, but Machamp was a creative and nostalgic enough design to earn its place as a series classic. As anyone would expect, Machamp is more than capable as a Physical attacker, and given its status as a franchise classic species, it's somewhat surprising that it hasn't gotten a Regional Form since the mechanic was introduced in Sun and Moon on the Nintendo 3DS.
Combining the Pokémon's Fighting Type with something like Steel could make for an interesting dynamic both competitively and aesthetically.
Eevee
Namely from the Kanto region, Eevee is easily one of the first Pokémon to come to mind when it comes to new evolutions specifically. Its gimmick is the "Evolution Pokémon," as ever since Eevee's first appearance in Red, Blue, Green, and Yellow its had multiple branching evolutions.
The affectionately dubbed "Eeveelutions" are some fan-favorites in Pokémon, and it's odd that it hasn't received a new one since Sylveon in X and Y on the Nintendo 3DS. There are still plenty of unused Types that Scarlet and Violet can and should take advantage of.
Arbok
Arbok certainly isn't among the strongest Poison-Type Pokémon, but that's precisely why the cobra deserves another look in Scarlet and Violet. In of design, Arbok is simple but works, and it also looks like a fully-realized evolution line. That's why a new Regional Form would likely suit it best.
Along with some stat buffs, a brand new Type combination and a fresh coat of paint design-wise would be more than enough to make Arbok more combatively viable and become visually exciting. So far, its popularity as one of Jesse's staples in the classic days of the Pokémon anime hasn't translated into the games.
Pinsir
Pinsir is perhaps one of the more creatively-designed Pokémon of the Kanto region, but it's also been left in the dust. At least for the most part, as with other Kanto species, Pinsir did get a Mega Evolution in X and Y. Unfortunately, like with some other clever and fun game mechanics, Game Freak scrapped the concept in the very next generation.
If Mega Evolutions are truly done and dusted, a Regional Form in Scarlet and Violet would suffice. It would be a great opportunity to give it a new design and give it a dual Bug/Fighting Type, as it has several Fighting attacks at its disposal despite inexplicably missing out on that Type in both forms.
Nidoking
In every generation of games, there's always a handful of commonly-used Pokémon for playthroughs. When it comes to the Kanto region games, Nidoking certainly fits the bill. The reason for this is that the male Nidoran could be fully evolved into Nidoking before even taking on Misty -- the second Gym -- since a Moon Stone can be found in Mt. Moon before reaching her.
It has an excellent and imposing creature design, and it deserves far more attention (with a Regional Form) than it's gotten in the generations since. Nidoking's design as it stands seems inviting for some creative reinvention as well as playing around with a new typing combination.
Nidoqueen
Should Nidoking receive a Regional Form in Scarlet and Violet, then Nidoqueen should be a given. She also has a great design in her own right, opting for less harsh features than her male counterpart.
It would make perfect sense to give her a Regional Form opposite Nidoking, ideally taking an aesthetically unique approach to her design and a Type combination that makes Nidoqueen stand out on her own . Likewise, though, it should creatively look like they're each one-half of a King/Queen duo like their current iterations.
Aerodactyl
Sword and Shield brought back Fossil Pokémon -- another fun franchise staple -- after Sun and Moon skipped out on them. However, while they introduced some competitive powerhouses, their anatomical mix-and-match gimmick left them with some jarring designs that missed out on some potential.
Should Scarlet and Violet not introduce any new Fossil species, giving classics like Aerodactyl a Regional Form would be an exciting shakeup. Given the pair of games' emphasis on the past and the future, this is something that could conceivably be worked in lore-wise.
Fearow
Having a designated Regional bird Pokémon is another classic tradition of the mainline games. It's an appreciated one, as most of these species make for reliable companions in playthroughs. However, Pidgeot takes the lion's share of the spotlight for Kanto, and while Fearow can arguably be better in battle during story playthroughs, it doesn't seem to get much attention overall.
It looks fairly complete visually, an argument could be made for either a new evolution or Regional Form. Either way, it could boost its battling prowess and give it a freshly exciting creature design.
Dragonite
Though it's a semi-unofficial tradition in name, each new mainline game has at least one "Pseudo-Legendary" Pokémon that earns that title from the community due to its impressive, borderline-Legendary stats. Dragonite is long overdue for some creative reinvention, and it was the first of its kind in of Dragon-Type evolutionary line and Pseudo-Legendary status.
Some might write it off visually due to its softer, slightly dopey design, but it could also be argued that its sweet visual approach is part of its charm. Dragonite looks like an amalgamation of dragons in folklore from around the world, and getting an aesthetic and statistical boost in a post-Fairy-Type world would be welcome.
Lapras
Inspired aesthetically by the Loch Ness Monster cryptid and the prehistoric reptile the Plesiosaur, the Lapras are a longtime fan-favorite Pokémon and one of the Kanto region's most elegant designs. It's one of those species in the franchise that balances soft and endearing designs with power, as Lapras are heavy-hitters in battle and have a versatile movepool. It deserves a bigger share of the limelight by now, with a Regional Form in the 9th generation.
Lapras did get a Gigantamax Form in Sword and Shield, but that mechanic was another one of the developer's more uninspired one-off gimmicks that rarely appear past the generation they debut in. Lapras seems like another design that Game Freak could afford to get creative with aesthetically, and perhaps pair it up with a Water/Psychic dual Type.
