Yes that's pretty much what I've wanted to do for a while. I have a little laptop where I want to install plan9 as the only OS. Plan9 doesn't have the drivers for the wireless card of that little fellow, it would be an offline device, like a typewriter with sed and awk, if you will.
I would use it to write everything I want to write, and only perhaps plug it via ethernet (I'd have to bring the router all the way to the computer for a little while) to upload to wherever I want to upload. I am thinking, however, that I'm unlikely to upload most of what I write in it. It will probably stay there for no-one to see.