DTA,Kimber, T/C, Weatherby, Howa, FN, a bunch of AR10s, basically everyone US except Remington IIRC, a lot of hunting rifles as well as "tactical/precision" and 6.5CM is popular specifically amongst the PRS crowd which is the target market here
I mean I own a .260 it's great but for match/long range ammo doesnt exist except for stuff that costs twice what the Hornady CM ammo costs for some reason
I'd buy the hell out of a 6.5CM if factory ammo was available here for the ~$1 per round it costs in the US
.260 isn't going to die but it's going to lose out in popularity in "precision" circles to 6.5CM I think. There's very little reason to pick .260 over 6.5CM (unless you want a Sako/Tikka)