Curiosity and Suggestion For Champ Mastery

So champ mastery (currently) is just for show, which I find to be a neat feature to show what you play a lot of, but I wonder why it is only available to earn for Summoner's Rift, yet still shows on the loading screen for other maps (aram, TT etc).

Why not have the option to earn mastery points for other game modes that will display the same ribbon/icon whatever you want to call it in the loading screen for that game mode? It seems a bit odd when I load into TT (I play 3s a decent amount) and it shows a mastery of a champ from Summoner's Rift, but completely disregards all the time I've put into a champion on 3s that I might not play at all on Summoner's Rift. I still have a different "mastery" of said champ and understanding of them, just on a different map and game mode.

Does anyone else think this might be a neat idea, or would you rather just have mastery stick to Summoner's Rift only?