I have considered this option a few times.
The issue is that dbFront currently takes extra steps to verify that a specific file is in fact what it claims to be. For example, if dbFront allows the upload of a PDF then dbFront will verify that the file contents look like a PDF to ensure that a malicious actor can't upload an executable or other dangerous file type. This is important because files that one user uploads are often immediately available to be downloaded or viewed by a second user.
I definitely would like to implement a solution, but it would involve more than just listing out the valid file extensions.
NOTE: Please vote on or consider funding this Feature Request if it interests you.