but 2 still leaves open "how do you move objects to a new layer?" - this is best as an explicit user action. It's just "where does it live and what do we call it?"
I've been thinking about expanding "selection" with a new panel. Stuff like "saved selections list", "select all objects with same x (color, brush, type etc)"
As for moving strokes between layers, I have 2 ideas:
Reworking the duplication, where copying and pasting don't happen at the same time anymore. You press a button to store a selection in the clipboard, and then paste it around with a different button (can also be the same button but differ by being pressed and held)
Not touching the original duplication and instead just having some sort of storage "pocket" where you can store a selection and then extract it in a different layer