Migrating good, recent questions is perfectly fine, and here's what I think about migrating old questions:
Please do not request for migration of old questions unless if it's really, really off-topic on Stack Overflow (or elsewhere) and a very good question for our site. Borderline and meager questions should be left alone where ever they are. If the OP of the post is not around anymore (greyed out) or hasn't visited in 2 years, please leave them where they are. If there's an old and interesting question but not migration worthy in its current form (either because of poor details in the question or crappy answers), please just re-ask the question here in a better form and in a manner that makes it on-topic for us.
However, I don't think stuffing our site solely with questions from StackOverflow is a good idea. Our primary goal should be to build the site and spread the word. In that sense, leaving comments, letting users know about our site and educating them about the kind of questions that are allowed, etc., is a better approach. We should be able to get questions on our own without having to mooch off a different site.
Don't go by Area51 numbers; they're bound to make the community do stupid things. Those guidelines are really ridiculous, and are thresholds that were set based on sites like cooking/Apple/etc., and are not realistic for a niche site (see crypto/theoretical physics, etc. for a comparison). They understand that too, which is why you see sites launch even with 3-4 questions/week. The important criteria here is traffic. As long as that doesn't show an upward trend, a site won't launch despite having stellar stats otherwise. Case in point: UX, On Startups, RPG, etc.
Right now we need to focus on two things:
- Good quality questions & answers
It doesn't matter if we're still in beta or have a sketchy theme as long as people say this is a place that they can go for good signal/image processing answers.
- Growth in traffic
This is a long term goal for us to eventually launch into a full fledged site. Remember that sites can remain in beta for as long as they want provided there's a good user base to ask/answer questions. Other than getting a dedicated theme (which would be cool), I see no other benefit to graduating.
signal-processing
andimage-processing
questions would get migrated to where they belong. $\endgroup$