I love Supergiant Games titles like Bastion and the rest have nearly all their music be Diagetic and in case with Transistor is neccessary for the plot.
The key apparently is because Darren Korb is the in house team working on day 1 with them.
I would love to see more musicals have their songs more Diagetic or immersive as a result, and would love to see more films integrate music better rather than treating it as post production stuff or leaving the temp music in.
To paraphrase Roger Ebert in his Grave of the Fireflies essay, in live action you feel for the person on camera. In animation it’s the idea or concept that affects you, which is much more emotional.