> The problem is that being "flatmappable" very strongly implies that it's a container

Can't fully agree with that, although I see your point. "Mappable" doesn't imply a container more than Functor's fmap method implies that all functors are containers. And "flattening" something is basically Monad's join.

But still, even if "FlatMappable" has a strong container connotation, I think it's good enough for establishing a first intuition. I think that once one shows what flatMap looks like in terms of e.g. Promises, the notion that it's about arrays or containers will vanish pretty quickly.