2018 Update - less than 50 questions were migrated away this year, so this seems to be low hanging fruit to make any changes. Roughly half the migrations away were to Stack Overflow, so that’s the #1 destination for migrations as has been the pattern for the past couple years.
The moderators here can and do migrate things to any site that accepts inbound questions - just pop an "other" flag with comments that you want it to be migrated to another site (especially if you have reputation on that site or have cleared the migration in the destination chat room before flagging). In reality, our site doesn't have enough people to migrate a question without moderator intervention and with the new timeframe to migrate things - most questions will just get closed as off topic and not actually migrated going forward.
Just to put some data behind the rationale - in the last 90 days our site migrated three questions. One to this meta, one to SuperUser and one to GIS.
For the calendar year 2012, we have 19 question migrations outbound:
- 6 - SuperUser
- 5 - Our Meta
- 2 - Stack Overflow
- 1 - Unix, User Experience, Server Fault, DBA, GIS
Of the 19 migrations, not a single one was done by users without moderator assistance. Even a slam dunk migration like the 5 questions about the site that users can surely self-migrate to our meta are not being seen and migrated in practice by the users of the site. If we find a large change in these migration numbers - it might be worth bugging for a code change to alter the user-migration sites, but I would expect the developers to remove any user migrations based on our usage statistics and not add them.