I'm hitting a problem sometimes when posting a question on a Stack Exchange site. The question is most appropriate for a specific site, but often the knowledge (i.e. the people) are grouped on another (Stack Overflow?). There are plenty of questions addressing this as a problem:
And plenty more. It occurred to me that while specialization (through fractionation of Stack Exchange to multiple sites) is a good thing, but only if the specialists spread themselves around. Often a grad students or scientists can contribute to Stack Overflow, math, the other math, stats, maybe another site etc. The problem most have a main or a couple of (science) sites they enjoy contributing to, and won't be aware of questions on other sites. For me Stack Overflow seems like an aggregation of such knowledge, making it very annoying to ask a statistical question that will either be answered within a day on Stack Overflow, or closed for migration - depending on luck - while posting on cross-validated may not get more than a few views over weeks.
Allow [tag:tag-name] syntax to link to any site almost addresses this, but that would require both a lot of effort when asking a question, plus you need to know to link to other sites particularly.
I ** (previously - edit below)** suggested making tags cross-site as a rule, that is, changing the default rule when registering to all site. This way subscribing to a tag will alert to any related question on any site - and maybe entice a pro who wouldn't normally visit to contribute. Tags are a loose grouping as it is, and it seems a shame to force someone asking on growth rate of some bacteria to miss out on advice from people on mathematics exchange. I can't see an advantage to dividing tags to sites either - if you don't want to see minecraft alerts in your feed, don't sign up.
If you think this is a bad idea I'd be interested in what advantage is there to keeping tags split.
PS: Maybe adding the fake Internet points as a cumulative sum (in addition to per site) can help as well, but I don't think it is as important.
Following the comment by @rene, I suggest creating default tag groups, so when registering to Python on Stack Overflow, you would register to Python on SU and stats (for example) as well. I suggest this as a default behavior to allow new contributing users a global view by default of suggested tag. No one is going to use filtering by default, not to mention looking for possible relevant cross-sites. This can't be universal, since Python may appear in a future cool-animals.se site - inspired by the Apple comment of @rene.