Microsoft also ported to Itanium, how did that turn out when customers ignored it en-masse despite all the World's OEMs pushing it ? Windows dropped Itanium support a decade later. MSFT is only using ARM to get into phones and tablets not because it wants to replace x86 in its traditional markets.
Itanium is an excellent example, basically little AMD beat Intel and all the big server OEMs pushing the incompatible to legacy apps Itanium and forced Intel to switch on its AMD x86-64 extensions in Prescott. Intel was not stupid enough to put all its eggs in the Itanium basket and believe it could force customers to use certain processors which the ARM OEM's will find out if they try and push ARM into notebook/desktops/servers when it is uncompetitive for those markets. Of course it's obvious why some OEMs like ARM , they can all pretend to be cpu chip makers now ;-).
You don't think tablets and phones will be 64-bit eventually ? You need 64-bit to have more than 4 GB of memory in even your consumers devices. After the A15 and A7 there will be no more ARM A- application processors that are 32-bit. 64-bit ARM is not going to replace x86 in its traditional markets, customers will laugh at it when they see the A57 benchmarks compared to Haswell or Broadwell. Laugh very very loudly ;-).