That's a great idea!!!! =D
Running is way OP...
hahaa, all jokes aside, I am sure its something they [Devs] would like to add, but as others mentioned, it is, and I would agree, pretty low on the priority list. I usually run, and I find myself trying to remember when I wanted to walk and couldn't. However... I do know a thing or two about programming. That walking framework is in there already. Would take a few lines of code to implement plus a keybinding constant. BUT, hours of proper regression testing to make sure you don't break something completely unrelated by accident.