Since Belle has a tendency to leave Rumple whenever he’s on his “better” behavior, and while that might not be an objective assessment of Belle’s real preferences, I do suspect it factors into Rumple’s perception of what she likes about him. Which makes me think that he probably doesn’t think it’d work, but who knows, I can definitely see the show going in that direction.
Another alternative is that I wouldn’t be surprised if Rumple, who is at his “darkest” in this season, takes the serum because he feels that the weak/light part of him is slowing him down. And then it’ll be up to Spinner Rumple to actually step up to the plate.