@hierarchnoble I understand. It's a risky topic. I actually don't think anyone has been too fired up in this thread, which is awesome! Let's talk data!
And you are remembering correctly about Reverberate. It happened on October 8, 2013. Here's a link for ya:
But, just a few days prior, Mark also said: "The Reserved List actually says we won’t print identical cards."
And, more recently, Mark is at least willing to play around with the concept and consequences of non-functional substitutes as shown here: (FN)
The "Spirit" of the RL, to the extent it's even a thing, appears to be applied in an ad-hoc way and is not subject to strict definition. As far as I can tell, it's a feeling-based test about whether a card is just "too close" to another. But, as examples like Helldozer show, even that is not a barrier to printing reasonable substitutes (even improvements) on RL cards.
FN = You can tell he's being glib and talking off the cuff because his idea, Snow Duals, actually does violate the stated RL policy. So, we don't take this TOO seriously, I don't think. He's just thinking out loud.