I wish #mastadon saved drafts of posts client side. Mobile web does not guarantee that a page will stay. Especially on lower end phones with lower memory, tabs go away. Which means thoughtful posts disappear, and people who take a while to gather their thoughts into words are disadvantaged.
Why just client side? Because most of the privacy issues are nonexistent. I expect a tiny snippet of JavaScript could be added as part of theme if main clients do not add it.