What I think is safe to say is that every bank is likely to have different anit-churning rules.

Chase's 5/24 has not been copied by any other bank. (BofA's 2/3/4 is about its own cards, not about cards showing from other banks on your credit report, like Chase 5/24 is.)

Amex's oncw in a "lifetime" has not been copied by any other bank.

Citi's 24-month lockout on card opens and closes (but not caring bout cards kept open) and its tying that to programs instead of specific cards has not been copied by any other bank.

Ignoring counts of hard pulls (which some banks have using for about a decade or more), no other bank has yet followed Chase into officially putting a fixed limit on how many cards you can get from other banks before they'll deny you. (There are hints that BofA may have some YMMV limits of that sort, totally separate from their bofA-only 2/3/4 rule, but it's apparently not fixed like Chase's 5/24.)

One of the areas where some people feel it's getting worse (and fear it may get even worse) is in the increasing YMMVness of it. For example, years ago Citi had a fixed limit of 6 hard inquiries (on whichever bureau it pulls) in the past 6 months. Now it's N in 6 months, with the N being YMMV. Also, Citi used to have a fixed limit of no more than 2 applications in any 60 (65) day period; now for some people it's n more than 1 applications in any 60 (65) day period, and until you run into that limitation you don't know if you're one of those people or not!

Another thing that could change (but no one knows if it will): The "invisibility" of business cards. Business cards from most banks (Discover and Capital One being the main exceptions) don't appear on EQ/EX/TU credit reports, which is what Chase uses to evaluate 5/24. But they do presumably appear on (more obscure) business credit bureau reports, it's just that no bank has yet chosen to pull those when checking for something like 5/24. But could they? Would they? (Or would it cost them too much per application?) We do know from experiments that Chase doesn't even count its own business cards against 5/24 (which they would only need to look at internal records to see). So does Chase not count business cards against 5/24 because it doesn't want to, or because it hasn't figure out how?

... Meanwhile, historically speaking, individual bonuses are bigger now than they used to be, which partially may offet the anti-churning rules. Over a decade ago, when it was possible to apply for 2 Citi AA cards at the "same" time (using a "two browser trick"), about 6 times a year, and get the signup bonus each time, the highest Citi AA card signup bonus was 25k miles. Now it's common to find 60k miles (sometimes even 75k), so with one signup bonus you get what you used to need 2 or more signup bonuses to get.

Oh, and don't forget that these anti-churning rules may be layered on top of one another. While 5/24 is only about 3 years old, for a decade of more, Chase has been denying singup bonuses (without denying the card) if you didn't wait 2 years since you earned the last bonus and have closed the previous card before you applied for the card again. That's still there, for those who are under 5/24, but 5/24 is layered on top of it, so you have to satisfy both rules before you can repeat a Chase bonus. (And rules related to counts of hard pulls, which usually aren't published, are yet another layer.)