Sidenote: It might be, that I am alone in feeling the need for this feature, as I am a wordpress developer and hence mostly hanging out around / answering questions tagged wordpress, php, javascript and jquery.
3 kind of questions: I notice three types of questions asked under the wordpress tag, which certainly goes for other tags related to separate SE network sites as well:
There certainly are questions revolving around wordpress development that indeed fit better here at SO than they would at WPSE. Namely those that are mostly php, mySQL and/or algorithmic questions that happen to have come up in a wordpress environment. I am far from suggesting that the wordpress tag is obsolete, even though there is WPSE. (see an example of this type of question)
A bunch of questions fit on either site - those that are true coding questions (php), but heavily rely on the wordpress API. The abundance of php knowledge of SO users is far greater than on WPSE (both due to individual skill level as well as sheer user numbers), the API however is much more well known to wordpress power users hanging at WPSE. Those kind of questions I wouldn't be sure about where to best ask myself. It is best decided individually, I guess. (see an example of this type of question)
A third kind of question still gets asked on SO with regular frequency that would much better be asked at WPSE. Those are questions that can either be solved with existing wp plugins or via the admin UI, or even questions about a particular plugin or admin function. In most cases, the user who posted the question is not to blame - the "wordpress" tag exists, he or she might have even found SO by googling a wp related search term and might not know about the existence of WPSE. (see an example of this type of question)
The issue: Often I am fairly certain, bordering on knowing for sure, that a particular question would have much better chances of being answered thoroughly on WPSE. I feel reluctant to flag such questions for moderator attention though, if I don't have the option to make the specific suggestion to migrate it to WPSE. After all the questions I'm referring to are not spam, often not bad questions either. I usually handle such cases by commenting on the question and telling the respective OP that he or she had better try at WPSE and link to it. The downside of this is, that if the user follows the suggestion, the exact same question gets asked at WPSE and the one on SO remains an unanswered relic that for one clutters SO and also might be found via google by people having the same issue rather than finding the (hopefully answered) WPSE question.
The feature request: I'd highly appreciate if the option "belongs to this other SE network site:" was added to the flagging menu under "It doesn't belong here > off topic".
The discussion:
- Am I alone with this or would others deem it helpful?
- And while we're at it, just for me personally, any suggestions on a clearer guideline on where "type 2" (see above) questions ought to go?
Sidenote #2: Both webmasters.stackexchange.com and programmers.stackexchange.com appear in that list, "Programmers" having about the same amount of total questions as does WPSE, "Pro Webmasters" only half. Are questions migrated to those sites more often than to WPSE? I highly doubt it, but what do statistics say?
Sidenote #3: The above question examples are not entirely perfect, but taken from the last two days. Didn't feel like going through loads of archives.
EDIT, Stats: According to Jeremy (see comment), within the last three months, 392 questions have been migrated to Programmers (#3), 252 to Webmasters (#4) and 105 to Wordpress (#7).
site:stackoverflow.com "migrated to wordpress". Obviously, it won't pick up deleted questions, and might miss some. Just a rough estimate, but gives you an idea of the proportions. We'd need an SO user with 10k to see the real stats.