I'd actually forgotten about the second Null/Silv!
Your idea is actually ridiculously close to what I have planned, in my version Aether would have stolen Null back from Gladion, he asks the MC to help rescue her and then entrusts her to the MC once he realizes that she'd be safer with him.
Your idea is better though!
I like the extra scene too, especially Gladion getting annoyed about the MC fucking Lillie and Lusamine, I was thinking about adding Gladion to the Femboy list too, maybe he's a little bitter about being left out?