Facing only matters for a few abilities in League, and *most* of those have to do with where your *enemy* is facing when you use an ability (think Trynd slow, Cass ult, Shaco backstab).
I got Rumble in an ARAM recently, and I didn't enjoy playing him. I love the concept of Rumble, but there's a problem. Flamespitter sucks to use. You know where you want to spit flames, but having to face that direction to do it feels *really* clunky with the way League's movement works. Trying to damage enemies while avoiding cc and death is really tilting. I don't mind challenging mechanics, but I *do* mind feeling like I'm fighting archaic control schemes. Rumble's Q straddles the line between those two options in the most infuriating way possible.
The solution is simple. Just change the cast so you can move in whatever direction you want while Flamespitter's direction stays constant. Just like a Lucian ult. I see no downside from a design standpoint, though I'm *sure* it will need a damage nerf with that change (and I'm fine with that tradeoff).
Okay, I made my argument, so let's get some Rumble mains in here to tell me why I'm wrong :P