I really appreciate the idea that one can almost fully use SE without registration; however this opportunity becomes totally screwed up when the Q is migrated.
An unexperienced user (who was told that he does not need registration!) is out of the blue faced with registering at two sites and hoping for automagical association system to work. Moreover, he is left on his own since there are no automatic tips what to do and moderators on neither site can do nothing but squeezing instructions into comments in mostly inadequate places.
I think it would be much better if migrating was impossible in this case and thus this user would have just saw a closed question and an instruction to move to proper site and ask there again. (It seems like an unfriendly additional work, but on a bright side it gives an occasion to adjust the contents to the target site, which is often required. Moreover unregistered users frequently do this on their own when they see comments suggesting the Q belongs somewhere else.)