My opinion is that a Shifter would fill an Unarmed Focused Maneuver Specialist. With at least a focus on feats similar to Brutal Bully, Thrash, Knockback, Furious Grab, Crushing Grab, Guarded Movement, and Shattering Strike.
Shifting should be a focus as well; it's kind of in the class's name. Some suggestions made so far makes me lean into a Main Battleform Flow-State, similar to how Rage or Panache works; and feats and focus spells could lean more into Chimeric Morphing, like freely adding wings, or changing unarmed damage types(S/P/B). Adding flat damage would also seem appropriate so the class could more easily be represented by many different shifting concepts. Precision Damage for animal shifters; Elemental Damage for elemental shifters; and so on.
If we are going with that approach, I feel like EVERY feat (or at least feat line) should actually be its own transformation/pseudo transformation, where the shifter assumes a form/grows a part that does the action.
Grab feats would be growing tentacles. Shove feats would involve bull horns get traction on the target. Trip would be growing a tail and doing a sweep.
Some of that could easily be done with flavor text; but i agree that Thematic Feat-Lines would be more than welcome. The Chimera one, in my mind, would be for concepts like Suneater and Kevin Levin. Overall, partial shifting seems to be a popular choice, and was definitely supported in the base class and archetypes( even if the execution was less than stellar ). Leaning favorably into the Morph trait, and specializing in Polymorph, seems like the way to go IMO.
I like the ideas mentioned about role flexibility, akin to a Feral Druid, and mixing Morph traits to allow for a Nature themed problemsolver. It gives the class a little more breadth to it than just worrying about combat role.
Style Shifter was an Archetype that revolved around Partial Shifting. With how Stances work on Monk, what would some ideas be for that? Should they allow Morphed strikes to just merge with Stances; or give them class specific Stances that make use of Morph traits? The example they give in 1e is with a Style Shifter stacking Boar Style and Boar Aspect. I’m curious what people think.