News feed prediction behaves the opposite of this. It tries to predict your intent based on past behavior, but that is, as you say, not possible, and could likely be why the news feed is dying.
YouTube's UI prominently features search. So if my interests change and I search for something I've never been interested before, YouTube can show me a pretty good selection of videos and tune its recommendations for future viewing.
I will say, though, that all social networks seem to fail at weighting past behavior too strongly. Whenever I start a new account on a social network, I find it's recommendations are much more tuned to my interests, and those recommendations become less relevant overtime.
Biologically, I'm a new person every seven years. As a collection of varied interests, it seems like I turnover much more often than that - and I suspect the rate of turnover is different for everyone.
For me, FB is far too controlling. So much so that I have 10 groups that I've started to "organize" my friends and in a way build my own feed. It helps. But it still not what I want, mainly because a lot of people are not group share minded.
I don't understand why FB is spending soooo much time and effort trying to guess what I want when all it has to do is...wait for it...ask.
That's Google.
A recommendation/suggestion system should offer its opinions and the user is free to follow them or not. Replacing explicit user intent with inferred intent is over-ruling the user, saying that the system's decision-making is more important than the user's.
At the forest level most people are predictable, often to a fault.