For example as in the picture.
Editable from one place but so that it can be used many times.
Not only for functions but also for others. The visualization becomes cleaner.
Subflows are not suitable, since for each node with its own config, you will need to create subflows.
Subflows are the solution we have today and they work well for it. They give you a new node in the palette which makes it quick and easy add additional copies to your flows.
To introduce a whole new concept like this, we'd need to be very clear on why subflows aren't suitable.