It does what it does perfectly.
All these calls for to-do functionality, events planning, etc. Nobody needs it except the writers of these articles. Just use other applications for it. We don't need to shake up email just because you want to.
And if you want to explicitly invite someone to something, you mail 'em a calendar item, it picks it up, and you can very definitely stick it in your calendar. It understands a bunch of different calendar formats, even. I thought THAT was pretty much standard across all modern email clients?
Sometimes I wonder if the people writing these diatribes about how EMAIL IS BROKEN IT NEEDS CALENDAR/TODO INTEGRATION are still using Pine or something.
The real brokenness of email is the insecurity and spam, IMHO. Fix spam and you've done something. And good luck on that problem.
E-mail is not broken. People are unorganized and think e-mail is the right tool for the job. E-mail is essentially a communication protocol. Nothing more. I think the idea that e-mail is anything else is what is broken. Stop trying to make e-mail something it clearly isn't.
Changing e-mail, fixing e-mail, or revolutionizing e-mail boils down to a tee-up for these types of derivative services:
1) New whiz-bang client
2) New whiz-bang web-based client
3) New whiz-bang protocol that has 0% chance of replacing e-mail.
4) A segway into some other complimentary product
Generally, whomever writes a book called "Why Its You That Is Broken and How to Fix That and Stop Blaming E-mail" will make a billion dollars.
It may look inefficient, but it doesn't have to be 100% efficient - people are inefficient, live with it.