Loving Glaive!
Do you have any advice for homebrewing a Wild Shape talent for a druid character?
You could handle it in 2 different ways.
1. Make a druid version of the Keeper of Relics or Student of The Unseen University talents. Each creature they can transform into requires a fetish or rune stone rather than a relic or spellbook. This keeps the Item Slot system working fairly for everyone.
They can take the talent multiple times if they want a wide variety of creatures to change into. AND/OR, you can link the power of the creatures they transform into to the PC's Level.
This could get complicated real fast. Xanathar's Guide to Everything had a chart that showed a rough guide to what monster CR = character level I think? I might start there. As a rough guide I might say the PC can transform into a creature of the same HD, gain a nifty ability (darkvision, flight, extra attack, etc.) and if an attack was needed maybe say they do [HL]d6 damage. It lasts a Turn or an hour - whatever feels good to you.
2. A more OSR approach -and the one I would probably use - would be to create a bunch of talents that mimic animal attributes (speed, strength, claws, climbing, etc.). I wouldn't have the druid PC actually transform into animals/monsters, instead sprouting bloody fangs, or hulking out like a bear or whatever when they used those talents. Makes me think of the Shifters from Ebberon. It would be fun for them to become more inhuman in their "normal" state the more of these talents they possess.
They could still pick up a spellbook (rune) of flight or spiderclimb to transform into an owl or a spider, but then you don't have to worry about leveling those creatures with the character as much. Though you sure could, going from a sparrow, to a hawk, to a rok or wyvren eventually.
Those are my thoughts. Obviously, it's your table so there is no wrong way to do it.