I think the author is wrong, and for one very specific reason: Google+ is not Google's endgame. It is not their penultimate product. It's certainly an important one, and Google has put an awful lot of effort in to get it right, but remember - Google doesn't live or die by its social network like Facebook does. There is little to no incentive for them to cripple their engineers with some arbitrary requirement for deep Google+ integration. Where it'll make products stronger, I expect it'll be used. Where it won't, it...won't.

Google is competing with Facebook for mindshare and social graph information here, but Google+ could fail spectacularly, and people would just say "lol, Google can't do social" and keep using their other dozen market leader products. If it succeeds brilliantly, on the other hand, then people will have no _reason_ to use Facebook et al, because they're getting that need filled in the course of their other daily tasks which happen to include Google. To assume that Google+ is Google's most important product ever and that all future products will be beholden to it is to view Google as a social network company, which is entirely wrong. If Facebook was trying to launch an integrated search engine or a GMail competitor, then I would absolutely agree with you - those products would be inherently limited by the requirement that they tie into and feed back towards Facebook's core platform, but that isn't the case here.