Whilst preventing TextMate from opening non-supported files is welcome (change in b4):
TextMate will only open files from the project drawer if their extension is found in the Info.plist, or if they have no extension (hidden files like .htaccess are considered to have no extension).
This now prevents me from running commands on the file selected in the project drawer, as $TM_FILEPATH is the frontmost _open_ file. (I have a 'Test Movie in Flash' command as part of my ActionScript bundle, now broken, to be run on .fla files in my project). Any chance you could add another variable, e.g. $TM_SELECTEDFILE or something, so we can access these?
Also, why not allow these non-supported files to be opened by the Finder when double-clicking them? And having a Open with Finder command as well as a Reveal in Finder command?