I've hacked aria-haspopup="true" in myself, tested and it works perfectly. Unfortunately I'm having trouble figuring out how to add it *just* to the parent items instead of all items and also add aria-haspopup="false" to *just* child items which means that menu items now have to clicked twice to work.
Anyway, hope this can be applied in future or that this could help someone looking for a hack solution now.