Instead of using comments, I would link a forum with each xowiki page (and learning material e.g. in LORS), where users could start new threads or comment on existing ones, thereby effectively structuring the comments. Additionally this would make it easier to have "personal" comments, as you could allow users to post private threads, where only they have access to (but could provide others read access as well).
This might be a good way for collaborative learning, as you could post public comments on the Wiki based learning material which are public (normal forum posting) as well as "notes" which you only store for yourself but can easily share with your friends. For obvious reasons we should keep the private postings private though so no admin inheritance for professors.
If you would use Ajax, you could then have the threadlist only load in the background, once the page has loaded, reducing the waiting time for the user if he indeed is interested in viewing the threads.
Does this make sense for the .LRN users or is the experience that students do not want to comment on learning material (publicly / privately). In which case it might still be a good idea for XoWIKI itself, as the heise.de example shows.