I like the ideas as a form of tutorial. Maybe to overcome the issues pointed out above, it could give a badge next to the name like the World Completion and PvP one, that is character bound and only lasts for a set period of time and can be refreshed by completing the challenge again.
Also, to not scare off more casual players, instead of being directly correlated to instanced end-game content, it could be implemented as part of some living story release, and have daily/weekly rewards like the daily achievement, and maybe even sometimes be a task to complete for the daily.