Law is often tri-state. For instance, at one time it was not legal to sell property to black people in certain neighborhoods in the US, because of legally binding covenants. This is the first state: prohibited.
The law was changed so that such covenants were not enforceable. However, that didn't mean black people could actually buy property in those neighborhoods. The property owners were still free to refuse to sell to black people. This is the second state: not prohibited.
The law was again changed, so that discrimination in real estate on the basis of race was illegal, and a seller could get in trouble if the seller used race to decide who to sell to. This is the third state: protected.
Lack of case law affords no protection. It just makes it hard to predict the outcome in advance.
So even in a situation where a court would award damages if a case was filed and malicious or negligent harm were proved, I'm not really sure it makes sense to say that anything was "prohibited" in advance.
New torts are invented, albeit rarely. Every so often there's a new duty of care in negligence. There are, I'm sure, other examples and the point is this: the lack of case law wasn't much help to the first defendant to lose on that point.
If an ecosystem for adapting and jailbreaking phones or cracking DRM for fair use grows up, then it will start drawing customers in if that's what people want.
At some point some of the original sellers will realize that if they remove the original locks themselves, their customers will get their unlocked phone with less money (just buying price instead of buying price + unlocking price), and eventually the markets make the shift because they are no longer constrained by the old legal monopoly.
I'm actually fine with losing service contracts and stuff for jailbroken devices. What I'm interested to see is how much ammunition this actually gives youtube to say "fuck you" when media companies send cease&desist notices and takedown letters and such to fair use youtube videos and that sort of thing. If there are no consequences for that sort of corporate bullying then it probably won't stop.