I guess it depends on what you want to be able to do though...it seems like it would be fairly easy to add to the in-game main menu (i.e. when you press escape)
Yes, manipulating the main menu appears to easy, since it's exactly that: To edit an already existing file to add further menu items.
It's also very easy to expand your key configuration setup (as Terror has pointed out). That, BTW, would perhaps be a nice addition to your scripts, Egg (v3?). Might be helpful for some people.
Could in-game menus be hardcoded? No idea. Technically I'm certain it's possible, but I'm not sure you could make those work in TF2.