TBH I can see where it fits. The Donkey (along with the Mimas) is probably the most dreamy pushchair to push. It glides along amazingly well. I had a Cameleon at the same time as the Donkey and there is absolutely no comparison in the push. However the Donkey, however much the back wheels are the same width as the Cam, just feels large as a single. It feels odd having the basket on the side, and I was worried about people taking things out of the basket. The underneath basket is wedge shaped and is shallow along one edge, so isnt the best, although not the worst either! I sold my Donkey (had been a Duo) because it was just too big as a single to be realistic. But the Cam was also no comparison after a Donkey.
The Donkey feels so sturdy and good off road, whereas off road with the Cam is a bit of a compromise.
The niggles of the Cam include the 2 piece fold, the handbrake, the 2 fold hood which covers the seat, the poor access basket.
So in effect, I think Bugaboo have done right in combining the two because they seem to have put the best of both pushchairs in one package along with what looks like a swing away bumper and changing bag clips as well.
The price has to sit between the Cam and Donkey, surely? So its another option really. In some ways, I agree that it seems weird that the Cam3 came out, but equally, I guess some people will prefer the smaller framed, smaller wheeled look, and if you are building a set of pushchairs, then the Buffalo really takes the true single up a notch IYKWIM and closes the gap on the Donkey, which really is quite different.