TL;DR: Google will have to rewrite most of its codebase if they choose ARM based servers. ARM isn't gonna happen anytime soon.
Google is not going to use ARM server chips for at least next 10 years, if they decide to use them at all. Google has an extensive suite of cloud based tools which they will have to rewrite if they choose ARM. They will also have a rewrite most of their codebase to work with ARM, which is not going to happen anytime soon.
Intel's chips are getting more power efficient and even if Qualcomm comes up with an extremely competitive chip, Intel only needs to slash the prices enough to de-incentivize moving to ARM.