I had looked at that option, however, it has the side effect of additionally trying to parse the files (instead of only supplying keywords from the lexer).
My personal preference in this situation would be to return to CC's prior behavior of keyword suggestion for unsupported file types, adding a blacklist (instead of the current whitelist) which the user - or other plugins - could modify as needed. (This setting would be separate from the one you mentioned, which tells CC what types of files to parse.)