You might wish to review their Privacy policy, which inspires more confidence than Goodreads:

https://www.librarything.com/privacy

The site's also been around since 2005, so, that speaks well to both its longevity and its integrity. Of course, that's not to say they couldn't be acquired tomorrow and paywalled, but I think it unlikely.

I don't think I am particularly worried about a proprietary solution. If I am putting my preferences in the public, pretty sure I am giving up on some dimension of privacy. With books at least, it doesn't seem so concerning as long as the recommendations don't suck too much (I don't particularly rely on recommendations that much though). But of course, you never know!

You do realize this entire post here is about GoodReads discontinuing their API? And as a reaction to that, you’re suggesting moving to another provider that doesn’t allow exporting your data either.

LibraryThing has several robust export options and an API. As they also run small "actual" libraries that includes some interesting old catalog formats as well.

Not sure if you've used the APIs recently, but they have been disabled without warning since October: "Our APIs are indeed disabled for now. They will be re-enabled at some point but we don't have an immediate timeline for it, so I wouldn't expect them back anytime soon." [0]

[0] https://www.librarything.com/topic/325722