There are many, many protocols for exchanging messages, chats, files, etc. (basically, what e-mail does), they all come, get some traction, last for two years, then die (except maybe irc, but except for a few nerds, it's hard to get anyone on there anymore). Some get killed by google, some just get replaced by "the next new thing"... but e-mail still lives, and works, and does what is needed.
So yes, we really do need something better than email (and we have plenty of options), but it doesn't have to (nor will it any time soon) replace email.
Well IRC isn't really meant to be used for persistent communication anyway
People do not want email replaced. They may want a new thing enough to use it in huge numbers.
And then that thing has to endure long enough, be open enough to see even a modest level of trust email has at this point.
Also addressed here: https://news.ycombinator.com/item?id=25804869#25807379
(I'm the author.)