allow migration of disabled sites

Why would you like to migrate disabled site?

You probably want to check the site before migrating it, to make sure it works, so you will know if you should revert to some earlier backup etc. Otherwise you are doing something you can't revert easily and you will have to enable the site anyway, also to make sure it works without issues after migration.

I don't see any good reason for migrating disabled site instead of enabling it first :)

I think the best reason for allowing it is if you want to get rid of an old platform by upgrading all sites from one platform to another. But if you have a disabled site you then need to go through the steps to enabling before migrating and then re-disabling them again after migrate.

I think the issue here is why have a limitation? If migrating a disabled site can be done without causing problems, why not allow it.

Is this a UI thing? I'm assuming that there's nothing in the backend stopping us from doing this.

New features need to be implemented in Aegir 3.x, then we can consider back-porting to Aegir 2.x.

I just tried this and it seems to work "ok"-ish with this mini patch. (bases on 6.x-2.x and also applies to 7.x-3.x)

What I noticed was that the migrate went ok, but when I tried to enable the site afterwards it was left in maintenance mode (set in settings.php). Running a verify task cured it.

If we would like to support this it should probably be an 'expert' setting to allow this. And someone would have to check why the maintenance mode is left on.