The future Charles V?
Iirc her sister Mary was betrothed to him at the time of HVII's death, but HVIII decided to marry her to Louis XII of France instead. As Margaret was older, her marriage might have gone ahead before their father's death.
She's too old for Karl V,
but (and this is based on a Philippa Gregory idea), Margaret was apparently considered for Louis XII ahead of Mary, but then went and married Douglas. I've seen her offered to Fernando II of Aragon as a second wife, as well as to Christian II of Denmark. Chances are though, that she's going to end up as a second wife to whomever she marries. Maybe if Anne of Brittany dies in childbirth, Margaret will be considered for Louis (if he's still king of France) here.