What you've alluded to is actually how people will interact with nearly all services in the future, through a proxy. Great effort is taken by social media sites to make it difficult to migrate off. But what they, and their investors, don't want you to know is that eventually these services will be reduced to API's that your proxy (an intelligent agent) communicates with.

Proxies already exist for linking your Twitter and Facebook feeds, and this trend is going to continue and possibly one day even replace the WWW we use today.