For me this all boils down to this ticket https://community.mendix.com/link/space/mobile/ideas/4970 -> If I cannot pass lists for edits into sub nanoflows, then I will need multiple return parameters. I'd say it's an either or thing, in which I understand that high-code devs will prefer 1 return parameter with changable input lists in Nanoflows.
Can you look the concept of return structs? This would allow us to "compose" our return with different kinds of return items (please permit all of the parameter types we also now have as inputs). Maybe a return struct can also be a domain model artifact that we can compose there, and then use as return type in MFs or NFs, or maybe even from pages now we introduced variables there?