I believe that the powers that be at Stack Exchange have said that they will only add a vote-to-migrate option if there is substantial evidence in favour of it.
So what I suggest, is that if possible, you collect a list of all the questions over the past few months that you believe should have been (or were) migrated, and then present them here on Meta and let the SE staff make a decision based on the raw numbers.
Here are some basic stats on the actual migrations over the last 90 days. Items in italics are vote-to-migration options that regular users have:
- Super User: 62%
- Stack Overflow: 12%
- Webmasters: 5%
- DBA: 4%
- Unix & Linux: 3%
- Apple: 3%
- Ask Ubuntu: 2%
- Meta Server Fault: 1%
- Wordpress: <1%
- Web Apps: <1%
- IT Security: <1%
- Programmers: <1%
- Android: <1%
- meta.stackoverflow: <1%
So based on that, it actually looks like DBA would be the next target - however, 80% of migrations are doable with the current migration paths, so I think it would be a hard press to get them to add another path.