There's no point PMing anyone about it - it's already posted here where we can see it fine. ;3
There probably won't be new rarity tags added for quite a while, as we already had one big rarity shift when the OMG so common rarity tag was introduced and currently the system is working reasonably well with the ones we currently have. People will always want more rarity tags to narrow things down further and further - we could have a thousand listed rarity levels and there would still be a wish for more. However, the rarity tags aren't meant to be precise markers of exactly which pet is worth what, especially since demand features so heavily in trading, and are more just for very general assessment of value.
List pets aren't necessarily rarer than non-list pets - they're just valued higher because there are fewer of them in circulation, which makes them functionally rarer even though there may be just as many of them as a less popular pet. The Black Advent and BMD are good examples of this, as they're no rarer than any other Advent but are vastly more popular and harder to find than most of their 'siblings'. The reverse is also true, as there are some pets that by rarity alone should be high on the list and yet aren't even on it due to low demand. Really, any pet that's a VR should probably be a list pet, and the only thing that keeps that from being true is availability, which is partly due to demand and partly due to age, as older pets are more likely to be in permanent homes instead of up for trade. There's no way to measure availability, and so listed rarity and functional rarity will almost always be different no matter how many rarity levels there are visible, and adding more levels might just make it more confusing. For example:
Person 1: "My dog has a rarity level of 80, so it must be equal to your 80-rarity dog, right?"
Person 2: "NO!!!!! My 80-rarity is equal to a 150-rarity because it's got a popular line edit. Yours is only worth a 50-rarity because everyone got tons of that dog during its event, and that was the common one of its litter, too."
Person 1: "But... they're both 80s?"
Person 2: "Rarity number doesn't factor in demand - go look at the rares list."
See my point? Adding more rarity tags when value is so heavily influenced by other factors wouldn't really fix the issue, and might just cause more confusion and irritation because it would look more accurate and yet you still couldn't trade 'VR for VR' or '80 for 80' because rarity isn't the same thing as value.