To me, not having a pre-migration check like looks like an attractive nuisance.
I mean, it basically encourages users subjected to post ban / quality filter / 50 question/month limit at one site ("abuse target") to intentionally post an off-topic an another site ("abuse transport") in order to overcome imposed limitation by means of off-topic migration to abuse target.
- a recent example of "SO-targeted" off topic question posted at Programmers as a means to get round a 50 question/month limit: https://softwareengineering.stackexchange.com/questions/116507/native-string-mathing-algorithms
note above was caught only because user was forthright about the intent to trick the system "...I know that this site is not for question about algorithms, so I will post question here and please migrate it to stackoverflow.com, they made constrain to my account..."
This brings damage to both sites. Abuse target site damage comes from the fact that intended limitation gets broken. Abuse transport site damage comes from the need to deal with off-topic question.
Note how things supposed-to-be-punishment can be perceived as pure benefit from (ab)users perspective here. Indeed, they get their question successfully delivered to target site over the limitation that was intended to teach them ask better next time. As for being migrated from transport site, this means nothing for them simply because they did not intend their question to stay there anyway. If this is not an open invitation to misbehave then I don't know what is.
Given above, suggest to pre-check whether user is allowed to post at "target site" prior to migrating question. If it turns out that this is not so, suggest to keep the question at target site and close it as off-topic. This suggestion is intended to let (ab)user know that tricking the system in such a way won't work. Also this is intended to help detecting and blocking systematic abusers at transport site.
- It would be also helpful to indicate that closed question was "blocked at migration" so that readers at abuse transport site would not have to wonder why some off-topics stay and close and similar others (those coming from users not subjected to block) gets migrated.