This is inappropriate for the following two reasons:
1 - This tracks users who are not logged in to Discourse, who have not done anything to accept being tracked by Discourse, and who probably have an expectation that they are not being tracked by visiting the site.
2 - This tracks user behavior when they leave Discourse for other sites (whatever the link goes to) and not just on Discourse itself.
From a big-picture perspective, almost all tracking can enable some cool feature. I have written about this before . Hence, the existence of some cool feature is not enough of a justification for tracking to exist.
As a general rule, a website should not track users in a way that is not obvious to the user at the time that they will be tracked. For example, tracking who posts a comment and having a list of all the comments you have posted under the user profile is acceptable because a user expects the website to keep track of that when they post a comment, so the website isn’t tracking them in an unexpected way. Tracking which links you click on is not an expected way of tracking, so if a website wanted to do it there should be some obvious warning, that requires an opt-in, before that tracking is implemented.
Another general principal is that users who are not logged in should never be tracked.