Garling suggested something happened to old Marineford. IMO, it would make the most sense if Dragon seized it.
That island is in paradise. Meaning once Luffy reaches Laugh Tale, it would be directly in his path to Mariejois.
Also, nobody else would really care for marineford. Teach is after the ancient weapons and one piece. So are the other yonko. But Dragon would care, as he is a former marine, and hence the island is likely symbolic to him.
Ultimately I’m guessing Marineford will be where Luffy meets up with Dragon, before they raid mariejois together.