I think you are overly hopeful if you think there is consensus on the different meanings of function and subroutine. Very few languages support returning more than one value from any kind of function or subroutine, and many languages conflate the terms subroutine and function, and/or use function to include not returning an argument.
In any event, having multiple return values was a clear potential feature when I implemented the feature. I chose not to do it for simplicity. And I probably wont change that going forward.
There are clear downsides with having to return in in some sort of structure, such as JSON, since the value also has to be encoded to ensure the JSON is valid. But unfortunately, that is just what you'll need to do. In the odd case you want to return multiple values, I suggest you just relent and use Instance variables - we are not building operating systems here, structural programming methodologies do not need to be rigorously followed.