"UID" will refer to a user's unique identity, "EK" will refer to a user's encryption key (think password), and "DATA" will refer to anything stored. "#" pre-fix means the thing was encrypted with the EK cypher "password". "Service" will refer to a cloud host, whether mega, dropbox, google, facebook.
The following are the possible options:
1) IF service stores: UID, EK, DATA. THEN sharing is possible, privacy is null.
2) IF service stores: UID, EK, #DATA. THEN sharing is possible, by anyone who has the EK.
3) IF service stores: UID, #DATA. THEN sharing is not possible, except to you.
Options 1 & 2 are the same, the only difference is in 1) gov requests DATA, in 2) gov requests EK + DATA. So unless it is illegal for the government to request a EK, this is pointless privacy. If it is illegal, then all they have to do is change the law to make it possible, which come on, isn't hard.
Option 3, which appears to be what MEGA sports, is actually BETTER for DMCA/Hollywood/Records/Publishers/Distributors, because piracy is absolutely impossible.
Unless, of course, you share your EK. But this is not convenient for piracy, because the only way to share your EK is via a service. If the service does not encrypt the sharing of your EK, then the service can share your EK for you, like, to the government. If the service does encrypt the sharing of your EK (with another EK), then nobody else can receive it except you (assuming you have the other EK). Now repeat.
Now, here are the following options:
1) If you use a public service to share an EK and reference the DATA. Then this is no different from present day, the government finds the public record, sees it is an illegal copy of Star Trek, and issues MEGA a takedown.
2) If you use a public service to share an EK. Then this is pointlessly hard, because cross-referencing is essentially impossible. How do Star Trek watchers know this EK is fro Star Trek, and where the data is stored?
3) If you use a Private services to share an EK and reference the DATA. Then the service is indemnified from the government, unless you elsewhere make yourself suspicious enough for the government to issue a request to the private service, then issue a request to MEGA for a takedown. But this is limited, because only the people you share to can pirate it.
If you notice, 3 is not much different than if you let your friend borrow a physical DVD of yours. DMCA&Co do not care about this, because everybody has to to know somebody of relatively close acquaintance-proximity that has an uploaded copy. This is hardly piracy.
I want this to be big. But it is not. It is mega deflated.