Intriguing question... I agree with Mirrorcube for the most part, as long as we need to categorize things and give them labels the concept of a "domain" will be around in some form or another.
Extension-wise we might see some flexibility, kinda of like a first and last name. Domains might utilize a primary and secondary ID, so you could pick anything before the "dot" and anything after, as long as it was unique. (e.g. sams.house)
Domains would still translate to a numerical address system (most likely IPv6 for some time to come) This would allow for every device you use (even trivial ones) to be assigned a unique IP.
There will always be a need for
unique identification.
In the future I believe we will have a mass convergence of media, enabling technology to be truly seamless and integrated into our daily lives, for example a ring on our finger will be our pc/tv/communication device, with a choice of holographic/projection and voice activated control. Or just something as simple as a piece of paper we unfold and draw all our information into, then fold back up and put in our pocket.
Internet connectivity will be worldwide - complete wireless coverage, every household device bought will be internet-enabled and you will set a type of ownership on this device adding it to your personal "domain" and linking it with all the other devices you own in your personal network.
Networks might even evolve in such a way as to carry out real-time searching for your query through personal agents, so instead of searching a central database, the network IS the database (think your own personal Google providing up-to-the-second information).
Identification will still be required though to find this wealth of information, like a street address you need to know where to look, that's why however they change the method of access you still need a unique address system of some kind.
Hmm... no idea if any of what I mentioned will come to pass, but it's fun to speculate
