Hosting your own data is trivial
No it's not. For a reason you've already recognized but glossed over. Backups. Even really tech savvy users have a hard time keeping backups going correctly. And not doing so means you have to worry about hardware failures and software errors accidentally wiping out your data. Not to mention the growing industry of somebody taking your data hostage.If you want to remove the incentive for people to move their data onto a Provider who manages the whole protection, backup, and availability side of their data for them you will have to provide a user friendly peer to peer solution for them somehow that doesn't require calling the tech-savvy {brother,sister,uncle,grandson,...} to set it up for them.
It's a testament as to how hard that is that no one has figured it out yet. Dropbox is probably the closest in that they keep the data on you box for you and allow you to pay directly for the service. But they still have a copy of the data that they can access if they should have a change in priorities.