I understand why Canonical wants to do this product. The Linux desktop is, along with all desktops including Windows and Mac OS, declining in importance. Canonical needs to establish their presence on mobile and Edge us their best hope. But I don't understand why any user who is less than wealthy would want to pledge $700-$800 for a first-time device from Ubuntu. It's somewhat analogous to people wanting to pay $1500 for the Google Glass Explorer Edition, but at least Google Glass is in new territory, wearable technology. Ubuntu Edge is going to be compared to all the smartphone systems that have come before it, and I don't think very many people are going to find the case for running it very compelling.
Yes, Edge is supposed to be one device that does it all, but that has been tried before, most notably by Motorola and Asus, and their devices turned out to be expensive and didn't sell especially well. I don't think substituting Ubuntu's phone system for the Moto/Asus devices' Android would have made much difference. Solving all the hardware problems of the do-everything Edge is going to be the hard part, no matter what OS it runs. And there's the biggest hurdle. Ubuntu is not a hardware company. They are a comparatively small software distributor for desktop Linux with no known experience in hardware, mobile or otherwise. They are a big fish in the desktop Linux pond, but that's a very, very small pond.
What seems to appeal most about the Edge is that nifty slide-from-the-left launcher. I think instead of going all in with a new device with very difficult to solve hardware design problems, Ubuntu could have set their sights lower by offering their user interface design as an add-on launcher on Android. If that went well, they could fork Android the way Amazon has, to offer their own user experience, development environment and app market.
By trying to do the difficult-to-design hardware of the Edge along with selling people on their software, I think Canonical is trying to do much too much at once, and unless they get very lucky with the hardware, the odds have to be heavily against them.