Mark, was there ever any consideration to giving the "You can play any number of " cards like Persistent Petitioners, Relentless Rats, and Dragon's Approach the Basic supertype, then expanding the rule that lets you play any number of copies of a Basic Land in your deck to include any card with the Basic supertype? It would allow you to save a line of rules text for these kinds of cards.

But it causes different issues. Basic means other things than “you can play more than four”.

Have you ever considered making the "Basic" supertype be what determines if a deck can have any number of copies? For example turning Persistent Petitioners into a "Basic Creature". Clears up card space and would already fit in line with what the Basic supertype already does with basic lands and basic snow lands.

For technical rules reasons, Basic can’t have that functionality. Also, it’s important to note that deck limitations is a tournament issue, not a games rules issue. (The rules can say “any number can be played” on specific cards.)

"purplebackpack89 asked: I was really surprised that Red was the second color to get a Plague Rats/Relentless Rats-type card." Technically it was the third, since Blue got one in Ravnica Allegiance with Persistent Petitioners.

Good point.

Could we see a complete cycle for rat colony and persistent petitioners over the course of the next few sets?

I think we’ll let every color get a “you can have as many of these as you want” eventually, but it’s not a cycle and it isn’t on any schedule to happen.

im very curious about Persistent Petitioners, how come its the first time a card with the "relentless effect" is not in black? and does it mean there will be a chance that each color will have at the very least one card with such an effect?

The “play as many as you want” mechanic (what R&D calls “Relentless”) is not limited to black. It’s just the color to have the first two. Any color can have Relentless.