If you make a promise, and I rely on that promise, and I suffer financial loss, you're liable.
It's a good idea too. If you promise that a plan will be free forever, people should be able to rely on that promise. You might get beta tester, promoters, or whatever you want. If those people stop being useful to you, you can't just throw them on out on their bums. You're hosting their data, there's a cost to migrating that data away. If they've integrated with your APIs, it can be a high cost. If that what you'd like, promise "free" but not "free forever."
It almost never makes sense to sue -- it's just not worth it -- but a business which breaks a "free forever" promise is probably breaking the law, and in the era of the internet, is almost definitely breaking the law in some jurisdiction.
So short answer, probably no practical legal remedy imho.
[1] https://en.wikipedia.org/wiki/Consideration_in_English_law
Full ruling available here (in German):
LG Berlin https://openjur.de/u/870262.html, which was appealed by Facebook and then went to the BGH (highest court) which ruled in favour of the parents: https://openjur.de/u/2110135.html
Edit: Added links and distinctions between the different courts at the end.
Consideration doesn't have to be financial.
These things happen, and have value, but I wouldn't have considered them as "given as a quid pro quo" or "mutual promises".
> Thus, it seems to me that the content of the obligation of utmost good faith in the SPA was to adhere to the spirit of the contract, which was to seek to obtain planning consent for the maximum Developable Area in the shortest possible time, and to observe reasonable commercial standards of fair dealing, and to be faithful to the agreed common purpose, and to act consistently with the justified expectations of the parties. I do not need, it seems to me, to decide whether this obligation could only be broken if QD or CPC acted in bad faith, but it might be hard to understand, as Lord Scott said in Manifest Shipping how, without bad faith, there can be a breach of a "duty of good faith, utmost or otherwise".
https://www.casemine.com/judgement/uk/5a8ff77660d03e7f57eac9...