I've been thinking about this for a while - the depiction of a druid in D&D: Honor Among Thieves, for example, shows the druid Doric forgoing casting altogether, and only using wild shapes.

If you wanted to create this type of thing, I could see it executed one of two ways:
  • Specifically. You would still use the wizard/druid chassis but whole-cloth replace the "spell slot" and spellcasting features with "animal shapes" (or whatever you'd call it). At the beginning of each day, the druid chooses a number of forms that they can call upon that day. Unlike a spell, which is either instant or with some sort of duration, these forms can be flickered between these. I envision this acting kind of like how the Druid working in Diablo IV - You wouldn't have "attack" and "shift to a wolf" as two separate things, but rather the way you attack is by shifting into a wolf. You wouldn't have the "Dash" action as something distinct from, say, "shift into a deer" - you would be shifting into a deer as a way to dash. Shifting in this way would be exclusive, rather than inclusive - if you have Spider prepared and not Rat, you can't shift into a rat.
  • Generally. This is what I expected once Tasha's came out and introduced the concept of the scaling "beast of the Air", "beast of the Land" and "Beast of the sea" statblocks. Going down this route would make more sense on the warlock chassis - You have the ability to shift into different groups of things as "invocations". Each one of those shifts would be using around the same stats with different line-item traits that distinguish a cat from a badger from a spider.