New user here, don't really know anybody IRL who also reads these books, and late night musing got something in my head that I was so itching to discuss I just had to register to post this.
This is part question, part personal wild theorizing.
So I was thinking about how exactly Taravangian was able to stab Rayse, and this got me to contemplating what happens to a person's physical body while they are holding a Shard.
We know that when a Vessel dies their body appears at the location where their attention was currently focused (we've seen this with Leras, Ati, and Rayse), so my wild speculation is:
When one Ascends, one's physical body is stored in what is basically a pocket dimension within the Physical realm, and while Vessels can communicate with mortals in a variety of ways (like Sazed speaking to those with spikes, or Odium speaking into the minds of those he has Connection to) actually being face-to-face with a mortal involves pulling them into this pocket dimension and interacting with them using the Vessel's physical body.
This would explain how Rayse was able to actually be stabbed, because otherwise it doesn't make a lot of sense - since we know Shards can make avatars, and Odium is rather paranoid and defensive and while it could be argued he's just so arrogant he's never consider a mortal a threat that seems a bit of a write-off to explain why he'd make himself vulnerable in that way, unless it's basically the only way he can be in direct contact with someone.
But, a sort of pocket dimension containing their physical body would explain the Visions that Odium uses to show off to people, it also explains the Visions that Dalinar sees (if Honor created a little play inside his pocket dimension and it's kept open by the Stormfather), and it would also explain how Odium had a body for Taravangian to stab.