Franz I'm not convinced. I imagine it would be quite common to want to bookmark a post for future reference (e.g. archiving a useful resource), but not be notified about updates to it... While still receiving notifications for some other topics that you're currently interested in.
Again, bookmarking and following are actions which have two completely different intentions behind them. Even when you just look at the entity you are acting on – you are bookmarking a post, and following a discussion. They're not compatible, and we shouldn't try and force them into one.
That said, bookmarking is not a priority for a first-party extension as it kind of replicates functionality already built into your browser. If you want to save a useful resource for future reference, you can simply bookmark the page/post on your browser. I'm just saying, I think there's definitely room for an extension to be built by someone though.
Kulga Not sure if being able to follow a post would be very useful functionality in real life?