I hope it does go somewhere, as IMAP isn't well suited to mobile, and neither is webmail.
(Yes, I once wrote a mobile IMAP client.)
The definition of those terms is quite different of course today, so my statement isn’t meant to contradict yours. I doubt Mark ever saw a laptop, at least when working with imap. Imap was a real step forward at the time.
Some server support only basic IMAP and do not offer QResync and Condstore extensions. So to detect deleted move email you need to select entire email UIDs to see is it still there. A lo of unneeded network call just to fully synchronize client state.
I even do not want to start that some providers like Outlook don't offer UTF8 extension, so the cannot implement a good search for different languages.