Parmandur
Book-Friend
OK, this all makes sense and is sound reasoning. My only caveat would be, "as of now." Things can and do inevitably change, and the PHB presumably won't continue to sell as well as it is. Furthermore, they can probably eek more dollars out of people by coming up with an "expanded and revised PHB" - a 5.2 version of the book that doesn't invalidate or replace the 2014 version, but improves upon it. That would be the conservative view of what "6E" looks like, but it also could be 3-4 years out rather than the 50th in 2024.
As for evergreen, I'm thinking this is primarily about the game itself - the name brand, what D&D "is." Certainly having relative consistency with the rules is an important aspect of evergreen-ness, but there can still be subtle changes. The game can and should evolve, but it doesn't need to be radical changes we've seen in some of the past editions.
The specific example he has used for a model is Settlers of Catan: consistent core rules, thematic tie in releases (my copy is Catan: Ancient Egypt for instance).
In terms of rule evolution over time, I think AD&D and WotC D&D are neither applicable models: look instead to BD&D. Holmes to Moldvay to Mentzer to Rules Cyclopedia. That's about the level of change I think we will see, when they update rules.
He was *very* adamant that they will not do a "revised" rulebook. To the extent that he is saying the Ranger variants he is tooling with will probably be released for free.