In the end, the only way to “control your own data” in a meaningful sense in the Fediverse (ignoring the question of possible conflict between different licenses, see above) is to self-host an instance. But that requires a lot of technical expertise many people will surely not want to spend time to acquire to become proficient in. So even on GNU Social the “right to own your data” comes either as a vague promise or at the high price of much learning. Of course, if you like to learn programming languages and technical stuff, then this will be all fine and liberating. But for those who don’t, the claim that one “owns the data” comes as theoretical and detached as the intricacies of the Federation, with no real bearings on reality.
https://simsa01.wordpress.com/2015/12/10/some-reasons-perhaps-not-to-join-gnu-social-and-the-fediverse/ [simsa01.wordpress.com]
Also kind of funny that free software advocates haven't thought through the copyright and licensing issues around federating posts, when a clever trick of copyright licensing is their keystone GPL.