Adding the ranks you mentioned above would be a fresh journey for the Legendary members which in turn make them hustle for more merits in the forum, but it'll demoralize some lower ranked members knowing that the journey is yet too far to get to elite. I think the best method is to change the color of the last coins on the legendary member's account who manages to hit the desired merit and activity count for a new rank. Instead of changing names that'll be a better way to distinguish between different levels of legendary ranks. On the other hand, the bitcoin sign you suggested, has been set aside for the core bitcoin developers and that will cause some complication when trying to determine who is indeed a developer, or worked with Satoshi.
What we should also consider when talking about adding another rabk to the legendary rank is that am sure after a new rank is been added, there will always still be a new urge for more, which to me will make it seems a kind of competitive race as to who are the eligible legendary members to get there first, being a legendary already is good enough to proof that you've done a lot in the past that has earned you to that rank you are.
Like somebody said; it'll add to more qaulity post in the forum, but your response depends only on the mark of elegibility; number of merits, and activity. If it's kept somewhere around 20,000 merits it'll be a difficult task and only a few would strive for that as it seems almost impossible. But, if kept around 2k merits then over 150 members who have already earned 2k merits will be instantly promoted to the new level which won't make any difference anymore. Frankly speaking, this is just a suggestion and may not get implemented, and the fact it's not implemented shouldn't stop legendary members from investing more knowledge into the forum. I mean earning merits looks good regardless of the rank a user found himself. So, legendary members shouldn't reduce the quality of posts because the ranking level ended there. In case a new rank arrives then it won't be a tedious task for them anymore, that is if shifted to a long merit number like 20k or 30k merits.