1. pretty sure Amazon is the only worldwide bookseller. but even there, the ASINs change for different markets. look at how isfdb has to have a different Amazon link for a book across different markets.
2. bookwyrm is nice for adding comments directly to book records... but... it can't do threading across books like that. the only comparable feature there is Lists, and that doesn't federate off bookwyrm. it doesn't have great hashtag support yet either. and it's absolutely shite for things you can't directly attach to a book. authors, series, genres, etc none of those allow posts. i can't even make a standalone post. basically, I'm saying bookwyrm isn't great for the kind of discussion you posted.