I guess it could be added, but I'm not sure it needs to be. All signal/image processing aspects of CV are by default on-topic and welcome here. The machine learning and statistics aspect of it might be better served on Stats.SE, although I wouldn't close such a question right away. By the way, computer-vision is our third largest tag.
Re: merging of the proposal, if the CV folks want to merge here, they're more than welcome on DSP.SE. On the other hand, if they weren't for merging, then I'd suggest giving CV a chance to be a site on its own. Having seen Area 51 proposals folded into others because of topical similarity, but otherwise having entirely different goals, audiences and more importantly, a possible pre-existing community, I'll say that people aren't generally happy about it (and sometimes, are even bitter). The chances of them being active here after folding when they were "this close to beta" are slim to none (because this is "not their site").
On the other hand, if they were given an opportunity to prove themselves, but failed to, for some reason, we'll gladly take them in our fold and house them under a tag (just like Go -> BCG, ML -> Stats). They're more likely to stick on at that point, because there already is some time and effort invested and they've seen for themselves first hand that they couldn't make it. If they do make it out there, well, then good for them. We all benefit from it either way.