I can imagine instead is a separate tagging function for bookmarks where an user can set up to X (maybe three) tags for his own bookmarks. Afterwards the bookmarks could be ordered or filtered by the tags and one could get additional search results from the bookmarks (marked as such).

That would be good. I know you can rename them at the moment to somehow organise them but it soon gets out of hand if you bookmark a lot without having a filter.

Now I'm not sure if it's too technical but having a symbol show next to a bookmark if there has been another post to that thread since you bookmarked it? then be able to filter only bookmarked threads with new posts?

Again I don't know how it would work but just putting it out there. Thanks