Answering the question as posed, sure. It could replace the PC for some consumers. The HPX3, 950/XL, or Galaxy with dock, could replace a PC for some consumers. There are two things I get right now out of my "PC", meaning desktop. It has an enormous screen, along with keyboard and mouse, and it has applications I cannot get on my phone, Visio, Access, Corel, Project (you know the stuff). I can already get a ginormous monitor/keyboard/mouse hooked up to a phone. What I can't get are those applications. If I didn't need apps I couldn't get on a phone, sure, it could replace a PC. The performance is the next consideration, but phones are getting pretty amazing. If I put an HPX3 and dock in a small desktop case and had people try it with a monitor/keyboard/mouse and told them it was running Win S, I bet most would believe it was a budget desktop.
I think the next question would be, would I want to? There was a time when I wished for one device, so I wouldn't have to move things around, because the latest version was somewhere else. With the cloud though, that isn't as much of an issue. You can get to your stuff regardless of what platform you started it on, or what you want to use it on if you try. So, my phone and my PC are different tools for different needs, and I don't mind having more than one. Even if my phone could do everything my laptop does when traveling, I'd still likely need the stuff to make it a laptop, screen (8-10 inches unfolded won't cut it), keyboard too at least. If the stuff that provided that, the HP Lapdesk, NexDock, was $150-$200 bucks, I might go that route and hook the phone to it. As it stands, at $600-$800, I can just buy a laptop.
So, could the unicorn phone replace a PC for some people? Sure. Will it? Probably not, IMHO.