This is a brilliant theory! I love it. But Vasher does mention that he is only a cognitive shadow nailed to a body. So I wonder if the Divine Breath is still available. Of course, he does still have regular breaths and uses them easily on Roshar, so who knows....
Just because there were no spren on Roshar doesn't mean they can't be used in the process. All things in the Cosmere use the same tools, Intent, Connection, Investiture, etc. Just that every Shardworld has different ways of accessing it. I certainly think sprens have something to do with it. Possibly why Akinah is shielded from High storms and thus can have no stormlight that isn't carried in physically.
Wonder what would happen if a Bondsmith tried some action in the protected space.
I don't think Dawnshard is investiture. Because Investiture is relatively common in the Cosmere. And supposedly anyone has the potential to use it. Besides, it was used to shatter Adonalsium, and it is known that that was a special tool.
A "Command" then is clearly different. And I wonder what the 4 Commands were, that were then each split into 4. I wonder if the Commands directly created the 16 Shards then. Is Dawnshard=Shard?
Is Rysn then a new Shard? Was that how all the Shards were created? Each absorbing a Command like "HATE" for Odium and "DESTROY" for Ruin, etc. Is that why we haven't seen all 16 Shards? Are some still waiting to be picked up and used?
And my favourite thought, is Hoid so obviously a Dawnshard himself? Someone once said that the same thing used to shatter Adonalsium is also the thing keeping Hoid alive. So obviously, he is a Dawnshard holder. No?
Yeeet!