IMO the most sensical low level* economic model for digital things would be one where you pay a really tiny amount every time you derive value from something. A fraction of a penny each time you play a song, each time you edit an image in some software, each time you visit a website.
There are a boatload of obstacles to getting to a model like this, but as a thought exercise it's really interesting to consider an alternate universe where this model got established instead of, say, everything being ad-based. Not only would it provide a model for monetizing software, it would also for example completely reframe DRM (making it both far more ubiquitous but also far less antagonizing to the user, since it would be aligned with what the user is trying to do instead of being at odds with it).
* The idea being that this low level economic would exist but for practical reasons (like overcoming human psychology) you might need to overlay a higher level model like a monthly "unlimited consumption" subscription or tax.