eg:
Idyllshire and by extension Shire gear. At the start of HW, main class was already past 60,so any fear of steamrolling HW content was not valid : blocked by MSQ
Ishgard: Can be reached from ARR cities by airship: blocked by MSQ.
Kugane: Can be reached from Limsa via docks: blocked by MSQ
Really, these areas/maps and more,blocked purely for 'story' reasons. Hypothetically, being able to go to those areas, would only break "story immersion" for the individual player.
Interestingly, Shirogane is not blocked by MSQ. As long as you have either a friend or FC with housing over there(estate teleportation). In some ways, I consider that to be breaking "story immersion" even if housing areas are not part of the 'main story'.