Such a site will never fit within the scope of Stack Exchange's style and mission. Shopping questions just don't fit well into the Q&A model, but they can fit in if they can be reworded into a question. Most of the proposed questions on that site would be fine on Super User if rephrased in the form of a problem/solution, e.g. "how do I do _________" instead of "what software does __________".
Furthermore, closed question messages are not the place to promote an Area51 proposal. Can you imagine if you were a brand new user, just asked your question, and were immediately told "oh, sorry, you can't ask that, but if you want you can get involved in a lengthy process unlikely to be successful in attempting to create a site that might someday accept your question"? Not user friendly.