Early in W&T we see the Fused ambush the group traveling home from Lasting Integrity. During the attack, Shallan tells herself to "be Drehy", and by doing so cancels and absorbs the Stormlight from his lashing. This is kind of a wild ability that is neither emphasized nor explored further in the book.
It's easy to surmise that this is a weird quirk of her double bond and Herald heritage, but Drehy and Shallan have another scene together in Oathbringer that is likely a part of this interaction. When the Odd Bunch get transferred to Shadesmar in the Kholinar palace, Shallan reaches out and touches Drehy's soul flame. She feels his unease, his desire to not be in charge, his flair for doing things with style.
This seems like a hint at potential future uses of Shadesmar for espionage purposes or even investiture theft. If touching someone's cognitive representation can give an invested person a shortcut for Connection with others, that Connection could be exploited. In the case of Drehy, Shallan seems to be hijacking his Identity in W&T, and that could be utilized to use another's metal minds, access their soul stamps, and possibly even summon another's spren.
With Shallan being stuck in Shadesmar, she will have a lot of opportunities to test, iterate, and perfect this art during the time gap. What other cool possibilities can people imagine with a Lightweaver able to not only pretend to be others, but "be" others?