It might have already been said, but there is inherently going to be a bias problem in determining which coins are established.
For example, I think everybody can agree that Litecoin, Dogecoin, and Ethereum are both established. But what about e.g. Solana which has market cap #3?
What about something like Bcash? [this will probably bring a strong no but then it's going to tarnish this forum's purpose as a "free-speech crypto discussion place"].
I think this point is one reason why exceptions will not be made to the rule referenced in the OP.
To somewhat piggyback on your point, establishing exceptions may make some view that the forum sees a particular (group of) altcoins as more legitimate (less of a scam), than others. Even if there would be no legal basis to this, there may be a moral/ethical basis, regardless of any disclosures made.
If there was a "neutral" criteria, there would be the potential for some to claim that the criteria is designed to include/exclude certain altcoins. Any neutral criteria would also likely require the reliance on third parties to make judgments, which leads to its own set of issues.