There is nothing impossible in this tech. world. If anyone provide quality and unique services then definitely that person or organization will be on top. NO doubt, Facebook is favorite social media sites but no one can predict about Google plus's future.
Social bookmarking, a single off-page optimization technique is not enough to promote a website. If you use only a single technique to promote a website then it looks spammy and not fruitful for ranking also.
According to my perception, it would be a good step to choose SEO to promote your website and to get more clients. Nowadays, online presence is necessary for every business to be a successful business.
I think, there is no need to fear with this update because it is for spammers or those who are using duplicate or poor content and building poor back links. I would like to say that it must be happen because with this update quality websites will get better ranks.