As mentioned elsewhere, we recompile everything at Google all the time. I'm not sure which things we've rebuilt with retpoline enabled. As Paul mentions in the article, the point is for software you believe needs to be protected, which may not be everything we build.
That thread on retpoline on Skylake has a lot of confusion. For some folks, they aren't 100% certain it works (it relies on understanding internal details of Intel CPUs) and they argue that IBRS on Skylake is cheap enough so "why not just always use IBRS and not bother?". That's the gist of this comment:
> personally I am comfortable with retpoline on Skylake, but I would like to have IBRS as an opt in for the paranoid.
I want to highlight that Paul and the team have had a lot more time to think about this issue than the folks just joining the discussion. Could our folks be missing something? Sure, and that's the point of public discussion and code review. We hope that over the coming weeks and months it's decided one way or another, but we believe retpoline to be correct and a good optimization (especially for older hardware).