There's much more to server hardware than CPU power and efficiency, and it's difficult segment to enter because of the risk involved making large investments in unproven hardware. But despite that, it still seems like things are actually moving in that direction and ARM is starting to get a serious foothold in the server market now. For example consider Amazon's new Graviton2 CPU's [1], which according to AnandTech 'puts all x86 alternatives to shame' [sic] when it comes to the price per unit of compute time it provides. I think it's entirely likely that the server market will be flooded with ARM servers in the not too distant future.

[1] https://www.anandtech.com/show/15578/cloud-clash-amazon-grav...