Alright, so you completed the last two rank-up missions with your squad. You even went further and hand picked your dream squad over the course of several weeks/months and got all the unique/standard members you were after. You got them all to 60 and tailored them to your liking. Perhaps you even got the precise chemistries you wanted, and also maxed out their mastery. You're also a captain now, got your emotes, and completed all the available dungeons with them, so what's next?...
… A test of might of course!
----------------------------------------
WoL: "You all have become so strong and have accomplished many challenging missions. So... let's see just how strong you all are. (Your nation's active chief) and I have come to an agreement for your next assignment."
Members from squad: "Hell yeah, we are up for anything! What's it going to be captain?"
WoL: "You are to face off against a high ranked member of the (insert your GC here) in combat."
Members from squad: "Seriously!? That's awesome! Finally! A chance to truly show we are worthy of being the squad trained under the WoL. Who is it captain?"
"WoL: Indeed it is. Your opponent is me-
Squad in unison: "WHA!!?" *panics*
WoL: "I suggest coming at me with intent to kill, or you'll fail miserably. This time on the morrow, I am your enemy. Prepare thyselves."
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
So as this suggests, acquiring the next rank will require an instanced battle with your squad. 8 against 1 like you're a friggin primal. And now is your chance to feel like one. Of course, I wouldn't gate it behind everything mentioned above, but I would suggest to make it so you do have to progress your squadron to access it.
I think the idea of this instance is to not actually defeat you, but 'push' you to the limit that you one shot the squad to end things. This is how they pass. So, my fellow Eorzaens. I ask for suggestions on how to bring this to fruition. Would you like something like this?