Right now ARM probably outnumbers x86 in number of machines running Linux by a very large margin. In my backpack there is one x86 machine and two ARM ones and that doesn't count the one that's in my hand
It all depends on what chips become available at what price. All cloud providers do lots of hardware design for their own metal. I'd they tell you that their next data center will be primarily ARM, they create a market for a million unit run of whatever CPU they choose.
As do the current top two supercomputers, Summit and Sierra, among others.