The question is ill posed. Let me transpose the problem to help illustrate:
All around the globe right now, there are amateur musicians going up on stage and giving their genuine, heartfelt rendition of their personally created music to a room of 8 people, half of which are half listening. Some of these musicians are technically incompetent and are unlikely to have a true market demand of any size but there are statistically, many people struggling who “have what it takes”, far more than actual slots in the industry to accommodate them. We know this because we know of stories of people who were plucked from obscurity into stardom and later fans took a retrospective look through their music and discovered even the early, obscure stuff was deeply meaningful to them.
If you look at this pattern of events and start with the hypothesis that our primary relationship with music is with the content, then this is a deeply startling state of affairs. We could all be listening to much better music than we currently are because we have not tapped on sufficient potential. We should be sending talent scouts out to every single bar in the world and devising cheap tests to screen out the worst musicians so we can properly evaluate how many “hidden gems” there are in the world and allocate them the prestige they deserve!
But there’s an alternative explanation that fits the observed pattern better: our relationship with art is mostly relational. That is, musicians plausibly need to clear some lower bar of quality to become famous but once they are famous, a large part of what we are engaging with is the fame itself. We listen to musicians because our friends have heard about them, they come to represent symbolic aspects of our identity, they represent tribal belonging to certain subcultures etc. There is limited space for fame in music because we have a finite set of relational requirements and every musical object we consume fits those slots first and the quality of the music influences how well they fit those slots.
There’s a second way music is relational: You posit that a relationship with art is similar to a scientific instrument assaying a substance and declaring independent variables like “funny”, “well acted”, “tight plot”, “exciting”. But a moment’s thought also reveals that we are changed by art as much as art is consumed by us. Art is what shapes our receptivity to other art, a Kpop album is deeply meaningful for an American teen who has consumed broadly from the genre but literal gibberish for someone who is encountering it for the first time. An American teen from 30 years ago would have had no entryway into Kpop, regardless of the quality. Americans had to be taught how to consume Kpop before they could even tell what Kpop was good or bad. An iPod that was handed to an American teen in 1999 with the world’s best 2026 Kpop on it would be meaningless.
You smuggle this assumption in from your description: “You can make a Star Wars film written by Scorsese”
You posit that the “Star Warsiness” of a film is a property contained inside of the pixels, that it’s meaningful to extract some durable essence of Star Wars and transform that with an essence of Scorsese to create a brand new art object. But the “Star Warsiness” obviously belongs much more to the social reception, that it became a cornerstone of nerd culture and the meaningfulness of it passed along generations and how saying the word Star Wars evokes a rich set of emotional attachments. There’s an alternate universe where Dune became the big blockbuster to do that and you’d be here, on this forum, asking the same about “A Dune film written by Joe Blow (who was a very big director in this universe)”. The pixels haven’t changed, so you can’t derive this quality from the pixels.
So the answer to your question of “What happens if an app appears” is: it already did. It was called the mass production of cheap musical instruments and a culture of indie performance. The impact was not nothing, we have a different musical landscape now than when classical music was commissioned by rich patrons and spread from the top down. But it wasn’t totalizing, it changed the position of various players in the marketplace, it didn’t destroy and remake a marketplace.