While on the topic of drafts, I have some other ideas, and I might as well run this by you to see if it's feasible.
I would love to have the opinion to "pin" drafts (to be used for templates for example), and for default behaviour to be that when you select an unpinned draft from your draft list, that draft is marked for automatic deletion if you end up actually pressing the "send" button.
This way you could have the best of both worlds: you can keep your templates easily accessible while your temporary reply drafts kind of clean themselves out automatically.
Don't know how technically feasible it would be to implement, though, or whether it'd be worth the hassle.