⭐ Merited by Rikafip (1)
If meeting the current Activity required for a Legendary is between 2 and 3 years roughly, meeting 5K would take over 13 years, and 10K over 27 years. Not much of an incentive in real terms, and seemingly more relatable to becoming an aged relic on the forum, so as to say.
Then it's decided, the new rank will be called "fossil" or "part of the furniture" 
. This sums it up really, its all about the ego and that's the one thing I noticed on all forums; after they spend a lot of time on some forum, some people start taking it way too seriously and even substituting real life accomplishment with the forum ones. I am not saying that all people asking for more ranks are doing that, but I've experienced that more than once in the real life.
While it definitely is something that artificially changes the way users act, it does actually provide motivation. When there's a limited rank that only a select few will ever reach, then some genuine users will be motivated by that. Unfortunately, you do have the flip side, where the status hungry users then try their absolute hardest, despite it potentially being detrimental to the forum.There's pros, and definitely cons to adding an exclusive type of rank.