concretely tho, it generally means hosting stuff on your own machine, on a connection you pay for. That's okay. But it's hard for non-specialists.
I think the way forward is actually to create standardized, easy ways to decentralize. The idea is shared by many and there's several attempts, although none seems to have matured enough yet.
Basically, those boxes and all allow you to store your data on your end. The part that's missing is that you need the devices you use today to be compatible. That means ios, android, etc.. have to be able to sync your pictures, movies, contacts, emails, what not there. That's the hard part.