This exists in Amethyst Drafts, and in long-form clients for long-form notes.

In Amethyst it'll save your drafts to your phone's local Citrine relay if you put Citrine's relay address in your "local" relay field in relay settings.  

 I think Nostur also has what I'm saying: when you click on the publish option, it shows you a window with the preview of the note and something like "Are you sure you want to publish this note ???"