Look at what we have now - basecamp, all kinds of free instant chats, group video chats, all kinds of organizational SaS, etc etc etc. Yet we still have ridiculously long email chains that often branch off and start to have a life of their own.
1) Everyone knows how to use email. Most employees don't want yet another way to communicate.
2) Your average office employee is pretty... average. And roughly half of the employees are dumber than that.
3) Training is expensive. One quick demo on a projector will not train your employees to use some new software. It's like half-life, 50% will learn after a month, 75% will learn after another month, etc.
4) You will always have employees who don't get this new software, many will probably not give a shit about learning a new tech, while they have a perfectly working way of sending a message. They will realize that when they change jobs, chances are, they won't be using this new software. But email will be there.
5) It is similar to the craigslist syndrome - it's awful, but everyone uses it, because... everyone uses it.
This simply isn't true. Most people don't know how to use email, which is why these stupid memes of "everyone hates email" and "email must be destroyed" persist. What people hate is email being used in a dumb way. Or to be more blunt: People hate dumb people. No surprise there, really. So a solution is to get better at getting rid of dumb people. One way to do this is to persist in using email well, and demonstrating (with persistence and persuasion) the better way when rolling across crap use.
This is one of those (rare) situations where the technology and infrastructure is fine; the people using it are the problem. Email can be incredibly effective when used correctly.
Mind you there are certainly email clients which make it far too easy to use email poorly.
Which is not to say that you don't have a point either, but rather just that your assertion of "simply isn't true" well...isn't true.
The conclusion is still the same. This won't solve the "problem" with email.
That said, my personal take is that you should start with kids. In contrast to the "dumb" people in the office, my younger sister's friends don't know how to use email. It's what their parents use (gross!). FWIW they use Facebook and a random collection of mobile apps for all online communication.
This is like saying I doubt people will be using phones 20 years from now. Email was been around for nearly 40 years It is the de facto standard for written communication between two computers and de-centralized systems need standards in order to work efficiently.
Although it was probably said earlier, the first time I recall hearing it was around 1980. It was "I doubt 2 years from now people will be using email." at that time. Maybe it wasn't exactly 2 years, but it was much less than 20.
Then it's soon the late 1980s, and we're still using some form of email. We hear, "I doubt 5 years from now people will be using email."
Quickly enough, we're in the early 2000s. Hotmail has really taken off, Yahoo! Mail is pretty popular, too, and Gmail will be coming along very soon. Nevertheless, people are saying, "I doubt 10 years for now people will be using email."
Here we are, about a decade later. Guess what? We're still using email, and more than ever. And what do I read today? "I doubt 20 years from now people will be using email."
I'm quite confident that when we're in the 2030s, we'll still be using email.
I agree with your comments about average employees. But perhaps this is changing? People are used to different messaging systems now, with various social networks and smart phones exposing them to better (or at least different) ways of communicating.