Not really. As they explain, they took great care to make sure that the output (and thus saved data) is in line with W3C mission. Maybe migration might be neede

Not really. As they explain, they took great care to make sure that the output (and thus saved data) is in line with W3C mission. Maybe migration might be needed in the future, but I see no reason why it would be any more expensive than migrating from WP (which is, btw, notorious for its storage schema choices).