Since I'm a developer, I'm missing such functionality for a very long time: to be able to highlight source files in the Lister. Most if not all of the modern editors have the ability to do this, even if they are not explicitely destined to work with source files. But I do not want to start an editor (which is usually a complex enviroment, much more then the Lister) each time I would like to simply glance at a file.
The plugin would maintain a library of text files in certain format defining comment styles, variables, reserved words etc, and the color for each of them. Upon viewing a file with known extension (C, CPP, PHP, ASP, JS, ASM, HTM(L), XML and so on) the plugin would apply a set of rules and simply color the text according to the settings in the library.
I think the way
Winsyntax does it is very simple yet powerfull (the KISS principle

) and could be cloned for such plugin.