Obviously not all questions can be considered questions of the criteria of one of the existing sites, and while Area 51 is allowing users to create new sites to help fix this, I feel that it will be hard to create one for every question.
Would it be good for Stack Exchange to make a general Q and A for questions that do not fit criteria for any site, or would it just be better to go on something like Yahoo Answers to get good answers for everyday questions?
A site without scope: that sounds like a pile of garbage. With no rules the quality will hit the bottom. Another problem might be that there is not a single topic expert that can answer your question.
A knowledge base of useful questions and answers can't be created by just one person: it needs an active community to do so. That's why the proposal to beta to graduation stage on Area 51 is important. And let's be honest: the site is not about you getting your answer. We want to contribute something useful to the world.
Our goal is not to create a home for every question; our goal is to make good homes for some questions. We're reaching a point of diminishing returns on new sites; many of the large subjects already have sites. It's a long-tail distribution of subjects.
It's simply not possible to enforce quality standards on an anything-goes site. As proof, see Yahoo Answers.
Stack Exchange sites feed off expertise. It's not practical to build a quality Q&A site that vaguely covers an infinite variety of disciplines. At the very least, you'd have to partition it out into sections for each discipline. You know, like sites.
There are a lot of questions out there that will never be a good match for Stack Exchange's model. Questions that just don't make sense or are too broad, for example.
For the questions that would be a good fit, but don't belong in any existing sites, I'd argue that there is a somewhat finite set of site-level categories you could vote for on Area 51, that would give you 90% coverage.
Just take your questions up a few levels. Instead of wanting for a site about handing nulls in C#, stretch out the scope into a programming site. Instead of one about late-80s BMW engines, try for automotive maintenance and repair. If you take out the scope a bit, there will typically be a point where you encounter a viable site-level category that contains a number of questions, but is still small enough to build a strong community. That's when you should post something on Area 51.
