While I understand that you don't want to break the ancient examples, it just pains me to see that there are no plans to drag Slick out of its current rather broken state...
There's no stopping you from doing this.
Feel free to write Slick 2.0 that uses proper design patterns and relies on GLSL instead of immediate mode. While you're at it, you can also rework image/texture decoding and handling, re-write the sound library, overhaul font implementation, decouple TiledMap and other extensions, etc.
But it will not be the same library -- it will no longer be Slick2D if the API is completely different. It may as well use a different website, different forums, different source control (e.g. Github, Maven), and a different name.
I'd like to see Slick completely overhauled, but I'm realistic. (a) It would take a lot of time and maintenance, (b) it would no longer be "Slick2D", and (c) the average user wouldn't notice a difference anyways, since many of them just want to make simple Tetris/Pong/Match3/etc clones.