Right now, the preview pane on the site will refuse to display plain text files unless the file extension is one of a short list of types. However, there's no good reason why this files can't be displayed. There's no need to try to syntax-highlight the files, just display the contents.

Since the site won't necessarily know if a file with an obscure extension is a plain text file or not, all files below a certain reasonable length in bytes should have a toggle checkbox in the preview pane ("Display raw contents" or something) that would force the file to be displayed as plain text. It would be a safe enough assumption to guess that the files are encoded with UTF8.

I know similar reasonable suggestions to merely add more supported extensions (e.g., .log) have been posted before and ignored. I'm making a broader request here because this is something I run into every day.