I have a patch that enables utf-8 request streams, and at the same time let me send binary files using the static file handler.
The idea is to open a (unsigned-byte 8) stream in the accept, then immediately replace it with a flexi-stream of type character with external encoding utf-8. After that, the stream can be reconfigured to unsigned-byte, for instance for sending the content in a file download.
A problem is that it introduces ainother dependancy, to the flexi-streams package by E Weitz.
Anyway, it's attached