I think it would be very useful for TextMate to identify the type of a script file based on the shebang line. This would be particularly useful for scripts without suffixes. In my opinion, an identification made this way would take precedence over one done based on the file suffix.
For example if the first line of the script named "do_some_stuff" was "#!/bin/env bash", then the file type would be a Bourne Shell script file and Shell script (bash) syntax would be turned on.