Firstly: Serious question..... Are you then going to separate leaderboards out along the demarcs you've made eg, Controller Only Leaderboard, KBM Only Leaderboard, Mobile Only Leaderboard. It seems very odd that you could end up with players on leaderboards that could never even meet in a game.
Secondly: Please consider not rolling it out everywhere until you have a solution for private games / custom servers or you'll likely kill off stream sniping to a great extent. Stream sniping may only be something you tolerate but don't care too much for but there is a decent, active and growing community on bedrock that participates in it with Streamers like FPSaltyRaccoon, PhilSwift76, (both of these stream almost every day) RelatedNoobs, RealJayCG, QuietMuerte, FXVoidz and a number of others that have decent and growing followings... I'd imagine it's in cubecrafts interest to help foster the growing streamer / youtuber communities rather than kill them off. I only realised yesterday that you'd rolled out the new system when I repeatedly failed to get into a snipe on the new kb then it dawned on me I'm controller and the streamer was kb/mouse.... most will just simply have no clue why they're not able to get in a streamers game or indeed into the same solos game as a friend for example.
Lastly, if you do go ahead and implement something like this then I really support the idea of being able to switch it off and make it optional with a default on rather than compulsory. If a controller player or a mobile player WANTS to play against KBM then they really should be able to. I would imagine anyone that's on a leaderboard will want to switch the setting off and be up against players on all platforms / input system; it's the diversity of levels, playing styles, techniques, quirks, differences etc that you come up against that helps you become a better player IMHO. If mobile players can only ever play mobile players they'll not have a clue how to battle PC / KBM players and never have a need to learn how.... I think that while those that only play casually will probably not care, I do think it's a loss to many others.
.....and erm.. dare I say it, please don't make a VR only category lol or I'm gonna end up roaming a very desolate and baron wilderness with no eggs to break or fights to be had.