when contributing code, the contributor can specify a strike price. if the upstream chooses to integrate it, then they're responsible for forwarding appropriate payment. this is one of the key motivations, ie to facilitate two developers to collaborate without prior discussions of financial details

and by the same token, the downstream is able to distribute directly (with or without source), and forward payment to the upstream, ie it's symmetric

if something like this license became widely used, it would make sense to adopt or build infrastructure to facilitate distribution of payments (perhaps licensezero ?)