Migration flags and votes should be removed from the close menu. Instead, along with "share, edit, close, flag" at the bottom of the question, there is a "migrate" option. When you click this, you will always have the option to migrate to that site's Meta page.
Beyond the meta site, however, the migration options are limited to sites for which you have a user account on (and there should probably be a soft-search menu in here for our particularly eclectic users).
More importantly, whether your migration vote counts as a flag or an actual migration vote depends on your rep on the migration target site.
If you're at 3,000 or more rep on the target site, your vote counts as an actual vote. If you're below this, it shows up in the review queue on the target site.
So for example, let's say I'm a Stack Overflow user with over 3,000 rep. I'm also a user with a DBA account with less than 3,000 rep, and a Code Review account with over 3,000 rep. If I see a question on Stack Overflow which looks like it'd be better posted elsewhere, I can flag it for migration to DBA (if that looks right to me) (which pops it up in the review queue for other DBA users with over 3,000 rep on DBA and SO to vote in agreement with my flag), or I can vote it for migration to Code Review (if CR looks appropriate to me).
Currently, if you try to vote a question to migrate away from Stack Overflow, you are presented with the following menu:
And it doesn't matter who you are, these are the five migration options you get.
And the fact of the matter is, I know I personally shouldn't be allowed to migrate to TeX or Stats. I don't have an account on either of these sites, nevermind having in the slightest clue what sorts of questions on are on topic there. Meanwhile, I do have a Super User account, and I do have a DBA account, but I have exactly 101 rep on both of these sites. I've never asked a question, posted an answer, or even so much as left a comment. I think I only created an account on these sites because I was thinking about asking a question or I wanted to upvote someone's answer (I have a use for these sites, but not much to contribute).
Meanwhile, there are other Stack Exchange network sites that have some potential for overlap with Stack Overflow.
- Android Enthusiasts
- Ask Different
- Ask Ubuntu
- Drupal Answers
- Electrical Engineering
- Game Development
- Information Security
- Server Fault
- Theoretical Computer Science
- Unix & Linux
- User Experience
- WordPress Development
This list only includes graduated sites whose designs have been completed. There are even more if we count beta sites (or graduates sites whose designs aren't yet completed, like Code Review).
But, I don't think all of these sites should be in the list either.
Compared with another feature request, I am primarily talking about the list of migration targets being dynamically generated for each member based on which other sites they are members of. If you don't even have an account at the target site, how can you possibly know that this question is better suited here than there?