Unfortunately I haven't been able to read all of the thread, but I wanted to throw in my 2 cents once again about the 2:1 ratio. I'm still worried about just carrying on with this rule, because it's really hard to carry out now that the site is getting older. I've made a few graphs showing what the various 2:1 rules imply for trading.
All of these graphs show how many pets
of equal rarity you need to trade for a pet a certain number of years "away". For example, a pet 1 year away would be trading 2022 pets for a 2021 pet. Trading for a pet 14 years away would be trading 2023 pets for a 2008 pet.
The colours show the different scenarios that are being discussed. Red is the standard 2:1 per year trading rule (pets double in value every year). Green is the 2:1 trading rule, but applied every 3 years (pets double in value every 3 years). Blue is the 2:1 trading rule, but applied every 5 years (pets double in value every 5 years). [1]
Here's the graph as my computer spit it out:

As you can see, the red bars are so overwhelming that we can't even properly see the green and blue bars. With the largest possible gap (14 years), you need ~16,000 pets to cross the gap. So that's 16,000 2023 rares to trade for one 2008 rare.
Here's the graph with the red bars removed, so we can see what the green (3 years) and blue (5 years) options actually look like:

As you can see, they increase much slower than the normal 2:1 rule. The 3-year option requires ~25 pets after 14 years, and the 5-year option requires ~7 pets after 14 years. I think even a gap of ~25 pets is quite a lot, but everyone has to make up their own minds on what they think is fair. Clearly, however, these numbers are more reasonable than the normal 2:1 rule.
Lastly: a projection into the future. Let's imagine CS runs for another 10 years, so that the max possible gap is 24 years. Here's what the graphs look like then:
With the red normal 2:1 rule:

And without the red normal 2:1 rule:

Notice that on that 3rd graph, the y-axis is measured in units 10^7. To cross a 24 year gap with the normal 2:1 rule, you need
16,777,216 pets. I feel quite strongly that this alone should disqualify the normal 2:1 rule from existence.
For the green 3-year rule, crossing a 24 year gap requires a neat 256 pets. For the blue 5-year rule, crossing a 24 year gap requires ~28 pets. That last one sounds better to me, but your mileage may vary.
To conclude: I'm still very strongly in favour of getting rid of 2:1. It just doesn't work. For better or worse, we currently seem to have a kind of "rarity math". I don't do enough trading to have a strong opinion on that concept as a whole; I just know I don't like
this rarity math. I do really like the idea introduced by Heda Vampiric of having an additive rule, though!
*+2 rule is when instead of 2:1 you just add 2 pets for each year different. Turns a trade into
1 2009 = 8 2013
Instead of
1 2009 = 16 2013
This would make the increases spiral out of control much less. I'm not sure whether +1 or +2 is the way to go, but I think either of those would work out a lot better than the exponential increase we deal with now.
[1]
Ok, so all of this is not quite correct, because the doubling should be calculated over intervals of years. Obviously pet values can't realistically be non-integer (unless we get real fancy with rarity math, I guess?). These graphs treat the years as more or less continuous for the purpose of visualization, because I'm too lazy to work out how python handles modulo arithmetic right now. Apologies! I may work this out in the future if I have time.
also apologies for poor axes formatting on graphs, all i can say is oop