Awfully big oeuvres to pick from, but I would say Heinlein is more likely since he's not selling as well as McMurtry these days. LoA can't compete with big commercial publishers for rights, I suspect.
Heinlein, god bless him, lacks the literary merit that LoA goes for. Plus they’ve already put one of his novels (Double Star) in the American SF series.
I think a volume is far more likely to be one of the stars of the American new wave like Disch or Delany (since they’ve done Le Guin and Russ).