Are you including all the plethora (eg. Thread) in the
discussion? Have you considered how threads merge with
synchronized? I don't agree that it's simpler. Thus, probably
we won't agree in the result of comparing both of them.
But it's nice to have several languages so that we could choose.

BTW, for closures and polymorphism you'd use module pointers
in Limbo; I forgot to reply to this earlier.