Though I do find your intent admirable, I think that it's misplaced - the reason there's no innovation on this front is because these sorts of time management tools are entirely dependent on the self-control of the persons they are targeted for, self-control issues being the reason they're glued to Facebook in the first place.
While such a time management tool may benefit a small few, the majority of people at a computer just don't seem to care too much - heck, even today many users need to be compelled to install an adblocker and to keep their software up to date -- imagine trying to convince that user base to also restrict their ability to go places online voluntarily.
Change has to come from within as an actual want - you have to want to be running every day to lose weight, you have to want to practice every day to learn an instrument or a language, and the type of change you're discussing has to come from an internal want to actually disassociate from Facebook and its ilk. Right now it's not so much that people don't want Facebook so much as they're not sure what else to do - the centralization of the web into a few major hub websites has left a lot of people completely lost as to what being online can actually do for you. You can see this effect all over the place - just watch how many people will upvote a "betterment" thread on reddit or imgur filled with free learning links, but never actually take the time to follow through on these threads. The few that do are the exception, not the rule.
As great as it would be if we all learned a bit more self control, mindlessly browsing Facebook is the new "TV on in the background" and has been for awhile.