I ended up deciding to wait it out based on my own gut feeling, and some helpful advice from several different people.
No shoes. Tanna will be confined in his 1/4 acre paddock (with Serts for company) until he can trot sound. Then he'll be turned into the 2 acre pasture until that hoof wall grows back down tight and together. In the meantime, I'm planning to go ahead and keep that hoof wall non-weight bearing, but not planning to cut it out all together. And I'll pack the crack with iodine-soaked cotton balls to keep it clean and debris free.
I'm also planning on doing at least one Clean Trax treatment or an apple cider vinegar/water soak to kill any fungus that might be causing this separation or might result.
Obviously no riding for him for several weeks, maybe months. I had some people tell me they couldn't remember how soon their horses went sound at the trot and at least one told me her horse wasn't sound until that hoof wall grew back down.
I am aware that Tanna's lameness may not be from the hoof wall separation. However, my vet believes that this is the most likely cause and we're going to wait it out and see if it is the cause. My vet and I are of the opinion to fix the obvious before looking for the rare.