+1 for dark theme or light theme option
and + some design suggestions:
Google Chrome is a browser, but I think it is a good reference for good minimalism. If following "full customized gui" then Sublime's top main-menu could be changed with icons.
If I get some free time, I'll make some collages in "paintbrush" to express some ideas.
This screenshot was posted by mvm of MS Intellipad in another forum. I just don't like that header in each page (looks like it's taking much space).
And Paint.NET's prompt. I commented that "preserve session" could be prompted on Exit.