The downside of our project approach was that we often got experts being very dismissive on re-using email and #OpenPGP ... and there still is some opposition which often subsides when actually trying #deltachat and #chatmail, looking at security audits and our strong usable security focus.
There may also be surprising upsides. The UK "Online Safety Bill" which attacks end-to-end encryption integrity seems to not apply for ... e-mail. Because everyone knows, e-mail is unencrypted, right? :)