Brandon has confirmed it wasn't Hoid who made the switch
He's also confirmed multiple times that Hoid does not have the blade.
As for Szeth's Oathstone, the idea is interesting!
https://wob.coppermind.net/adv_search/?query=Oathstone
We do seem to have an older WoB where Brandon confirms that the Oathstone has no magical properties, but it has been RAFO'd since. Might've been something Brandon changed his mind on. That WoB is also without a direct source.
but previous Bondsmiths couldn't use Connections, would the Shin have known how to? It also shakes the largest part of Szeth's characterization a bit: his fidelity to a personal code, which is what caught Nale's eye.
As for the Shin not coming to recollect the Honorblade, given Ishar's comments in RoW, they're busy with something else in their homeland. Possibly an Unmade. Why they even gave a Truthless an Honorblade is not known. We don't know enough about the Shin.