I like your idea. I'm not so sure about the drawing part, I've always thought that the spren were locked in blade and plate form simply because they didn't have a radiant bond. It could still totally be possible though!
I really like the idea that Maya is changing because Adolin is seeing her as a person, not a tool. Adolin's always kind of treated Maya like she's special, and this only increased when he saw her Cognitive form. Spren are so easily influenced by human opinions, so it seems like Adolin would at least have had an effect on her, if not been the entire reason she changed.