Form Master follows the file Upload Rule pattern designed into DotNetNuke. In situations where a Host sells Web sites to customers, this pattern, allows the Host to specify what type of file any of their customers can accept in any part of the application.
A developer creating a module which would violate this design pattern would be creating a security hole, and would be totally irresponsible.
If you are the host, and want to upload any type of file you, can always purchase the source code for the module and modify it any way you like.
This will never be a feature.