There's been some good discussion on Salamence so far and I think it's become clear that Mega Salamence for A+ is not as absurd of a nomination as it might sound, but I want to highlight a few other Pokemon I think are worth discussing right now. These have
not been voted on yet, these are just nominations so I encourage anyone to post any disagreements or additional thoughts. Expect a proper update closer to the start of the next season.
A+ -> S
Landorus-T has more or less picked up where Garchomp left off last gen as the premier Ground-type and with USUM its usage has only gone up. Landorus-T is incredibly strong and its versatility makes it very easy to fit on a team due to its ability to check numerous threats. While it's not quite as splashable as Mimikyu, Landorus-T shares a lot of the same traits that make Mimikyu an S rank threat. It doesn't command the same respect that Mimikyu needs at Team Preview, but the role compression and versatility it offers arguably make it just as prominent as the other S rank Pokemon.
A+ -> A-
Volcarona is essentially a less oppressive version of Blaziken, this hasn't changed at all since SM gave it a stupid amount of Z-Moves to abuse. That being said its presence has continued to dwindle, and I'd argue part of that has to do with the meta being increasingly hostile to setup sweepers that rely so much on actually setting up, as well as Stealth Rock usage staying consistent. It's still just as strong of a threat as it's always been but the rise in Charizard and Gyarados usage as well as AV Landorus-T becoming a more popular set make things tougher for Volcarona. Regardless, I don't think Volcarona holds up as an A+ threat anymore.
A- -> B
Mega Heracross is just not as effective as it was in ORAS with Thunder Wave support getting nerfed and Trick Room teams having a much better Mega option in Mawile, leaving Mega Heracross as an awkward in-between. Mega Heracross is still a fairly strong Mega with proper support but being a middling speed Bug/Fighting-type is really bad in a meta with Fairies, Fires and Mega Salamence around. This shouldn't be in A- anymore, there are better Pokemon for each of its roles at this point.
A -> A-
Primarina has never been my favorite and most people are aware of that, but I think the meta is even less kind to a less bulky and more offensive Tapu Fini. Naganadel's presence hasn't helped it at all, but its lack of physical bulk compared to Fini hurts a lot right now with so many physical threats around. Its niche as an offensive Fini doesn't translate as well to current meta unless you need its ability to hit through Substitute users. In comparison Fini is just a lot easier to fit on a team and fills more valuable roles than just bulky offensive Water/Fairy-type, so I don't think these two should be in the same rank.
B+ -> A-
Kartana has been a new favorite of mine since late SM but I think now is an appropriate time to bring it up with favorable meta trends resulting in more Kartana usage. Tutors barely changed anything for Kartana but less Salamence and Aegislash helps it quite a bit, and it benefits a lot from the general trend towards Mimikium Z Mimikyu and bulky Landorus-T without Superpower. It also has a favorable matchup against Gyarados which is all the rage right now, but that doesn't mean the stuff that ruins Kartana no longer exists. Fire-types like Charizard and Blaziken are still as common as ever and its awkward Speed tier without any form of boosting does limit its sweeping potential a bit. That being said I think A- is appropriate for Kartana now.