Just a contracts guy.
I'm all for this ruling. Changeable clauses like these ones have been used because no one said they coundln't be enforceable until now, so everyone threw them in, hoping they'd stick until someone knew better.
The problem with them is that Contracts are supposed to show a meeting of the minds of the two parties. Yes one can say that terms need to be flexible enough to adapt, and that one can agree to anything into a contract. Meeting of the minds, an intention to contract, and certainty of terms. That's the beauty of contracts, but these clauses are totally anathema to the concept of a contract.
Nearly anything can be changed: price, property. The benefits conferred (consideration) to either party are entirely adjustable by one party. Basically one party dominates the contract by virtue of their bargaining position (std form agreement), and ruins the exchange value of this contract. If there's ever a reason for unconscionable contracts, this is it (Unfair terms agreed by way of dominant negotiating position).
This even affects limitations of liability, and these are things that have traditionally held short shrift with judges. The basic concept is you can limit your liability to exactly (emphasis: exactly) what you ask for. No more, no less. With these clauses, you can effectively amend or retroactively(!) amend your liability or even jurisdiction clauses to be more favorable. There's already significant judicial debate about what a Limitation clause can apply to, and if it's properly brought to the attention of the other person. One opinion is that if the limitation basically destroys the value for one party completely, that's it is problematic for enforceability. The whole "we can change anything and not tell you" part flies entirely in the face of this.
I do think this ruling will be limited in some capacity. It'll probably be the agreement that the consumer was last made aware of. It'll probably need to include a mandatory walk-away period. We have those here in Canada wrt to cell phones and renting where you have a period of time to walk-away entirely if drastic changes are made. I think the rationale for this is that it builds a new contract effectively by performance. You know about the changes, and accept them by continuing to use the service or product. Knowledge is critical.
I am NOT a lawyer, I just have wierd reading habits, this is not intended for, or to be used as any form of legal advice.