That's the same as what people are calling a modular monolith, no? The key thing with composition is the bits sit next to each other, there's no inheritance or dependencies between the components. In my idea you'd have a bunch of "pure service" apps that are focused on individual areas of the business or processes. Then you'd have one or more UI apps (either user-facing HTML or APIs) that compose those services to do what needs to be done, e.g. a "create order" endpoint might compose the create order service from fulfilment and the send notification service from comms to put an order on the fulfilment backlog and send notifications. Is this what you had in mind?