Long time ago in the late 1990s, I was a system administrator, maintaining a bunch of SMTP (mail transfer agent) servers. Since 2007 I have quitted running SMTP servers at home. The number of SPAM messages have rapidly increased since then; 95% of my received mail messages are considered SPAM and unread now. I've been watching this on multiple mailboxes using different SPAM-filtering algorithms, and the trend is mostly the same. Only 5% of mail messages are meaningful to me, including those from my business partners and mailing lists.
On a DNS operator meeting last year, I was joking to one of the participants that the current SMTP (email) and DNS will cease to exist much sooner than we expect, due to the complexity of the running systems. People tend to believe they are always up and running, but the reality is that a lot of sysadmins are killing themselves to get the systems up and running.
I think DNS surely has a lot of economic incentives to keep it alive as it is now. For example, domain names are protected under intellectual property rights and the international treaties. So somebody will keep the system alive, although the implementation details may change.
On the other hand, many people have already seen the limitation of email; they are not pervasive as they were a decade ago. People are fed up with SPAM, and try not to rely on email too much. Many of them have already been using other messaging systems, such as the one implemented in various SNSes. In other words, they put a lower priority to email in general.
Some people say the easiest way to deal with SPAMmers is to constantly change the mail addresses, which I do not think so. I think SPAMmers nowadays exploit all the traceable resources of mail addresses, so the leading time you can gain by changing the email address is getting smaller and smaller every day. The hardest part to fix, and the impossible part to fix, is the promiscuity of SMTP, to accept everything without authentication. Many people have said this and I know this is a mere repetition, but it is a fact we must recognize.
Recently I tend to feel more than ever that I really don't care about the medium or protocol, as long as I can stay connected to the people who I want to. Of course it might get harder to meet new unknown people and communities, but I think that role has already been replaced by open blogs and the update notifiers or RSS readers.