I hate to say this, as much as I sympathize more with Netflix than a major studio, but shouldn't the studios eventually stream their movies themselves? Is the tech really that hard, why are they outsourcing it to Amazon and Netflix?
Like TV channels, we should just surf the studio websites until we find what we want (using Google, perhaps). That seems the inevitable future rather than one or two clearinghouses. That's what tech does: removes the middleman (except when there's a man in the middle ;).
Streaming can be hard, particularly if everyone is trying to watch at the same time. Witness what happened to HBOGo the night that they made the season finale of 'True Detective' available.
From what I can tell, the major studios do not want to be in the content delivery business. I don't see an 'inevitable future' of the major studios streaming their own content. I think branded portals to the studio content, outsourced to a small number of content delivery companies, is more likely.