Would it make sense to add Aviation.SE to the available migration targets for off-topic questions?
One of the key criteria for default migration paths is the level of migration occurring.
There's no "right" level for establishing a migration path, but tens or hundreds of migrations with a single digit rejection rate seems safe. Single digit migrations in the last 90 days and/or rejection rates that can order a drink without ID are signs that the path will be a waste of time to establish.
A 10K user can see the TSE migration stats, which show no out-migrations in the last 90 days except to Expats, which is established. A more comprehensive SEDE query for questions successfully migrated away turns up only five sites with five or more migrated questions since the dawn of TSE:
Site Count Latest Migration
Expatriates 117 2016-05-04 23:41:43
Outdoors 22 2015-08-09 22:36:13
Money 9 2014-06-18 13:34:29
Aviation 5 2015-07-07 15:30:28
SuperUser 5 2014-01-08 19:43:14
Since Aviation has seen only five questions from TSE, and the last was ten months ago, I doubt the powers that be will approve it as a direct migration path. Such things are fraught; many users suggest migrations that are inappropriate for the proposed destination but also not inappropriate for the origin.
If you do perceive a lot of questions that would be better-answered at Aviation, then we should step up our efforts to flag them and have moderators move them, and then we can make the case for community migration when the stats are more convincing that such a thing would be beneficial to both communities.