Three ways for it to become as mainstream as you imagine:
1. If Japanese studios start explicitly creating anime with more western norms, because of the larger market. This has already happened to some degree, and their declining population could make appealing to the wider market more important.
2. If Japan itself starts shifting its norms to be more like western countries. That happened after the war, and it could increase with the cultural trade brought on by instant AI translation, globalism, or immigration pushes to get the population up.
3. If western countries change to be more accepting of Japanese norms. Again, this is already happening, Japan is famously successful as exporting its culture.

Seems like all three may happen at once.