Expanding on this tweet: You could launch a super fancy social networking site with all the features that everyone expects, but built entirely on existing open standards:

• Sign-up: Pick a domain. This is your username. Register domain through service. Can be transferred out at any time. $10 a year is nothing.
• Profile: Hosted at domain.tld.
• Messaging: Email at whatever@domain.tld. User can use whatever email app they want.
• Social Graph: Contacts via CardDAV.
• Authentication: Done with Oath.
• Permission System: Entirely done with contacts. First pass filtering is done with spam filter. Email from non-contacts goes to message requests folder. Contacts can be marked using CardDAV groups and fields as "friends", which enables bypassing spam filter and seeing private items.
• Feed: RSS at https://username.com/feed.xml. Private items require authentication. Include email address in RSS metadata, and comment via email.