Core should have taken this advice much earlier. Users aren't forced to use a certain Bitcoin client. If not acting is not upgrading to 30, I'm all for this approach. At the same time, signalling the client policy you agree with also doesn't harm anything. To the extent that this is acting, it's neither a radical action, nor overly impactful. But it takes some power away from those acting without forethought (or worse, with it).