As far as I can tell, there are only 3 NatDex formats (and depending upon one's perspective, either 3 or 4 NatDex tiers) in Smogon's tiering system:



In addition to those, if you look at the page for
NatDex UU, you can see a list of Pokémon that are banned from NatDex UU but that (for whatever reason) aren't considered NatDex OU, which essentially makes them NatDex UUBL, despite the fact that that isn't actually a thing.
(Even regular UUBL sort of isn't a thing, but at least it gets its own page on Smogon.)

The reason I am posting this, however, isn't about these tiers, but rather all of those NatDex tiers that apparently don't exist yet, including NatDex RU, NatDex NU, NatDex PU, and NatDex ZU.
(There isn't a NatDex Ubers either, but I am assuming that that is intentional.)

So with a dexited Pokémon like Shaymin-Land, who was in RU in Gen 7 (rather than
UU)... what tier should I list them as being in in Gen 8?

It doesn't seem appropriate to list them as being NatDex UU since they were never UU in the first place, and I have no reason to believe that Shaymin-Land (or most of the other lower tiered Pokémon removed by Dexit) would've increased in tier had they not been removed from the game, but since there is no NatDex RU yet, NatDex UU is the lowest of Smogon's NatDex tiers ATM, so how should I handle these Pokémon?
(And it isn't just Shaymin. There are a TON of other lower tier Pokémon that were dexited, and the issue of what Smogon tier I should list them as being in in Gen 8 is a confusing one, to say the least.)

Just to clarify, this doesn't really impact my own tiering system itself since it is universal, but the listing of Smogon's tiers for these Pokémon (which is a key part of what I've been working on, to compare my tiers to theirs) is far more complicated because of this, and I need to decide what to list these Pokémon as.