Indeed I am also slightly weary of too easy account migration. Not only do instances lose character because of it, but also are much more likely to be shut down or abandoned if it can be justified with easy account migration. The instance I am currently on for example would probably not exist anymore had not the previous admin felt the need to hand it over to someone else.
But in the bigger picture I think Hubzilla's nomadic identity is a good compromise of balancing out these different considerations.