(. . .) thinking of hybridizing Pathfinder with 5E, although at this point I don’t know Pathfinder well enough to do so.
That's the side of the equation you find difficult to define?
Still, Ability Score Checks aren't really anything new. Don't most people still use them in a pinch when there's a gap in the rules?
As to scaling, you think the design goals are dictating *more* levels as a way to nod to earlier editions? We have seen a rise in (O)D&D, AD&D, 3,0E and 4E from 10ish, to 20ish, to 30ish+, and Basic was all about the stretched (I wouldn't call it "softened") leveling, so maybe that's the tack they will take, as it does make for more books and supplements more easily. We'll see.
"setting-specific themes that give actual mechanical benefits in addition to flavor" is really no different than class features, as used by PF, D&D and many other games. However, what you are proposing in tailoring a character concept and background, and having mechanics grow from that, is exactly what I'm doing in the project I am working on now, and this is the standard way to create each character, rather than attaching a laundry list of features to a theme as a way of creating "roles" or looking on characters as fitting into some predetermined theme-shaped box.
"Legendary" weapons or items are a fairly common device for having magic items grow with the wielder. PF isn't a whole lot different from 3.XE in regard to dependance on items, though any individual campaign can always buc that trend by simply starving the modifier beast and keeping the creatures and challenges stunted. In early D&D an item with such prpoerties would likely be considered an artifact.
I think you are right that this thread would benefit from the world turning a few score times but you'll know PF a lot better then too.
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