I think @jenstornell concerns are valid. If Kirby becomes popular for lots of use cases, at some point the community will need to address the performance issues that will naturally arise with trying to handle thousands of files.
There are different approaches to how one might solve this. One possibility is to have pluggable persistence, one user might opt to store everything in disk, another might wish to use a database.
Another possibility, which I find much more appealing, is to use databases for indexing content, so the real content would still remain on disk, but dynamic querying would be efficiently handled by database backed up rest services.
In the meantime there’s nothing preventing us from experimenting. I mean, if Kirby provides the hooks, people can implement the indexing/querying stuff around Kirby without needing to change it.