It is nearly possible to use the iPhone 5s as a desktop replacement; however, developers are still missing a crucial piece: the mouse api. Apple could add it now, but my guess is that they will announce it with big fanfare as an iOS8 feature, along with an update to the stock apps to support it and the iOS home screen with TV Out support. iPhone 5s is powerful enough for a thin client replacement, many apps and web browsing. Workstations will soon be only for developers and gamers. When people start ditching their workstation for a plug-and-play iPhone dock, Microsoft will tremble.
Right now, you need three accessories but it could certainly be built into one that would allow you to charge the iPhone while working on your desktop.
The current dock supports audio out and works with all apps.
You can use the VGA/HDMI adapter to connect to a screen. Apps can support it via the TV Out api. Many apps don't do it yet so the best is to set the dock to landscape mode to see everything on a bigger screen.
The USB camera adapter for the iPad seems to recognize USB keyboards and work with the iPhone. Otherwise, bluetooth keyboards are fully supported.
The Missing Mouse
The USB camera adapter can probably recognize a USB mouse and some bluetooth-enabled mice can be paired. But without any api to access it, we are stuck! The only option without Apple support is a custom Bluetooth LE mouse with a custom api, but then you will have almost no developer support.
Therefore, the only sensible thing to do while waiting for the api is to add TV out support to Vim or develop your own keyboard only web browser ;-)
Apple won't be the first, but, as always, full integration, simplicity, polishing and developer support will triumph.
The future is already here – it's just not evenly distributed. — William Gibson