[cryptonector]

Yes, the difficulty lies in having to deal with just-whatever-the-users-and-their-MUAs-do. It's a bit of a mess. But a bit of convention can be taught to users -- think of Markdown, which has been quite a success because it's just a bit of convention that users were often accidentally using anyways. A bit of convention can go a long way.

The real challenge is that the GUI MUAs often make it hard for users to use even a bit of convention in plain text... I'm thinking of Outlook in particular, but it's not the only one. Even with an MUA that does angle-bracket quoting the right way and encourages users to trim quotes and bottom-post, the fact is that editing plain text is difficult and boring for most non-vim/emacs users out there, and that is most users. This problem can't be solved by the author of TFA, but if the author of TFA solves the problems that are in their bailiwick, then that could add pressure on MUA developers.