Is it a practical application to use Bluetooth for file sharing? And is Bluetooth Mesh optimized for this application?
Yes. Bluetooth can be and is used for file sharing. There are many apps already available which make use of Bluetooth for file sharing.
Bluetooth mesh is an m:m device communication network primarily used for creating IoT solutions. This mesh network uses Bluetooth LE which is designed for short burst connections and many to many messaging amongst devices. It cannot be used for audio streaming or file transfers.
Ref: Bluetooth Mesh FAQs