After some consideration and long last, I think I've arrived at the successor Rule to my vaunted Rule 58: Rule 59!
Rule 59 to Poly is ...
"Potential dating partners must have a smart phone; preferably an iPhone."
Okay, here's my rationale.
In today's day and age, texting is important. It keeps us top-of-mind and allows us to have semi-quality discussions over a hand-held device. Yes, iMessage is powerful and it's free. That's important. Moreover, the full QWERTY keyboard allows for more thorough conversations even when texting. And a smart phone gives access to multiple forms of media - maps, email, video, web.
A smart phone just greases the wheels of a poly relationship. Defying Rule 59 is, like, well, "lacking lube". It's friction-filled. It's cumbersome. In every poly purse and every poly ... pocket ... should be a smart phone! It just makes the process of dating and flirting massively easier.