I am just saying who unless the pretty unlikely situation in which Richard has no so by Alys of France and had an extremely good relationship with at least one between Henry the Young King, Douce or their son, the chances of seeing the son of the Young King by his second wife as Duke of Aquitaine are really pretty low...
A better scenario would be Henry the Young King remarrying to Alys (but why? Vexin was also Margaret’s dowry and now belong to William and I do not remember what lands were originally chosen as her dowry)