This was just getting lost on the garden path, really. It's trivial if you have the concrete type, but the point is you don't have the concrete type.
I haven't come up with anything better than T: 'static on your reference-producing methods, assuming your base Ts are static. Any trait or boundable property that your base case Ts have but the produced &Ts don't would do.
Using T: 'static seems like it could be too limiting -- depending on SomeTraitT's implementations, since that would disallow things like Vec<Iter<'_, _>> or similar - i.e anything that contains a reference