I really wish we could kind of dump email as a technology, since it's really outgrown what it was originally designed to do.
What I'd like to see is mass adoption of Jabber/XMPP, since it handles IM stuff, along with tons of other features. I think it could probably totally replace e-mail, since most servers and clients support offline messaging, so you can queue up messages even when you're not online. Also, imagine how everything would change if you used IM for password resets or signup confirmations, instead of having to wait a few minutes to get an e-mail with your info, it would be nearly instant.
Another cool possibility I see with Jabber mass-adoption is authentication. You could develop (if there isn't already) a way for people to login everywhere with only their jabber id, and then the site could just IM you to ask if it was really you who attempted to sign-in. This is a lot like OpenID, except I think alot faster and probably a lot easier to implement.
XMPP solves many of the issues with email only because it requires explicit whitelisting of message senders, and because it's still a niche ecosystem compared to email. Most users don't even try to accomplish cross-domain message sending, much less extensive file transfers or server-side storage and archiving of messages, no matter what the server capabilities might be.
As a set of protocols, SMTP and IMAP are both pretty well-suited for the task they set out to accomplish. Furthermore, the delays you mentioned in message delivery are largely due to intermediate spam filters and store-and-forward queues, not inherent issues with email as a transfer mechanism.
Cross-domain messaging is easy, as long as you either accept all servers, or at least whitelist the ones you want, and have the S2S port forwarded, or better yet, no NAT at all. Same goes for file transfer, but I will admit I've never personally succeeded at a file transfer, but I couldn't get DCC to work either.
One of the big differences between this approach and email is that it would be a prompt-based system, instead of a switch applications and click the link. By prompt-based I mean that it would pop up a window asking, instead of you having to go look for it (and possibly open Outlook, Mail, or some other heavy app thats not running 24/7 like most people leave IM messengers)
I don't know enough about Jabber/XMPP to decide how well it could replace email, but email is plenty fast for me. For almost any website with password reset/confirmation, by the time I click my gmail tab it's already arrived in my inbox.
What I'd like to see is mass adoption of Jabber/XMPP, since it handles IM stuff, along with tons of other features. I think it could probably totally replace e-mail, since most servers and clients support offline messaging, so you can queue up messages even when you're not online. Also, imagine how everything would change if you used IM for password resets or signup confirmations, instead of having to wait a few minutes to get an e-mail with your info, it would be nearly instant.
Another cool possibility I see with Jabber mass-adoption is authentication. You could develop (if there isn't already) a way for people to login everywhere with only their jabber id, and then the site could just IM you to ask if it was really you who attempted to sign-in. This is a lot like OpenID, except I think alot faster and probably a lot easier to implement.