So, will we ever have a reason to actually leave a city at level 50?

[Tannlore]

I then wonder:

"How does the FATE in N. Thanalan benefit level 50 characters in a meaningful way? How does it aid in level 50 progression? How does it compare to past Chimeras that even dropped DL gear? What purpose does it serve beyond trying to get people to level 50?"

A minion, GC seals, Gil, an achivement. The question is more what value do you place on these things post 50? What would you like for him to drop to make it of value to you? Then realize, depending on what you want it to drop, he might be quite harder. Then realize if it is something good, you'll have a LOT of people there. Then... well look at Odin/Behemoth.