I'm sorry, but... since we have Dissidia & Kingdom Hearts franchise, I'm not going to close up the chance of having this grand dream happened. Especially now that SE has been working on FF7 remake which IMO is a huge risky deal. (we all know how majority of remakes do on market despite the decision SE made to pursue this)

BTW, you were thinking way too much on technical side, while I was thinking simpler ways. Like I said, I like to keep gameplay on each sides, just want the story segment happened. This IMO should appeal even to FF14 players who never tried FF11 before. Heck... I even had couple FF14 players who tried FF11, while they admit it's a bit outdated but they do like it. Oh... and as for me, I started FF11 after FF14 and no knowledge of how-to, and yet... here I am already finished almost all story content all the way to Rhapsodies with only few like Voidwatch that I've yet cleared (on Jeuno 2nd tier battle). This is all thanks to countless help from FF11's Bahamut communities that's been really kind to help me on many occasions. So what you thought of FF14 players not getting used to FF11 kinda misleading since I am one of that example. You can look up my achievement profile on both ffxiah & ff14's lodestone for proof.

Also, Cloud of Darkness is just one of the agent to the Void, which should be the one you should check in first place. Dissidia kinda hinted that this entity was responsible to events on almost every FF series.

So again, I will keep this hope in my heart that the joint venture of both Vana'diel and Eorzea (or should I say Hydaelyn now that 4.0 reveals the whole world map of it) may cross paths. XD