Since this game is not the “main serie FFXIV”, there is a very good aspect regarding it…the potential usage of other FF games content!
Seeing how flexible the original FFXIV is it would be pretty simple to do. But first lemme toss some area position examples…assuming the culture and development of each FF, it would be a defining aspect about its position at world map…let’s start with Eorzea…its somewhat medieval but, at its north, we have the garlean empire.
Due the map style we could easily place garlean empire as an “eastern europe”, also locally being known as East Aht Urghan. At its west we not only can put the West Aht Urghan but, after the ocean, Quon and Midarthia. To the north we can put Ivalie as “british isles”, that was already conquered by the empire, which explains the presence of the “garlean judges” there.
To the east we can keep increasing technologically, adding railroads and roads, which could connect many other FF games, like FFVIII, FFXI and FFXIII by railroads and FFVIII and FFXIII by roads. FFX areas could be reached by airship.
FFXIII Pulse itself could actually be merged with FFVII Gaia like a big continent, having Nautilus, Bodhum and the Cocoon (crystal pillar) turned to empire side (for access), the Gran Pulse areas in-between and then the Gaia areas at northern side.
But anyway…just like this we could also do to the battle mechanics…for FFXI skillchains, just add quested WS actions that can chain with each other. This, pretty much, would also engulf the combo system of FFXIV 2.0, allowing like each weapon type having 3 WSs that can be chained in a cyclic way (FFXIV combo) and that can be chained with another weapon WSs of this type (FFXI skillchain).
Materia system can be easily added, making materias generate actions that only appear when equipped to the weapon. Again, we can just make the quested WSs said above actually coming as materia.
FFVIII guardian forces can easily be added. We already have the “guardian deities” so we can simply make a junction pact system between you and the guardian to add a set of actions…or maybe another guardians…FF world is plenty of sets of divine entities…guardians, avatars, totemas, fal’cies, eidolons, aeons, etc. Very same thing about fal’Cie pact and summoner itself! In short they would be the very same thing but with minor mechanics differences! While summoners use multiple avatars to battle alongside, the soldier (class) would have just one role-based guardian equipped. Similar to FFXI BST familiars, you would need to equip the specific guardian to have access to it. Also, you wouldn’t be able to change guardians midfight so you need to pick the one that fits what you want best. The special feature here would be the presence of the SP bar (same one used by spellblade)…while class actions would be paid with MP and TP, guardian actions would be paid with SP. Each action would have its own cost and you would have the summon action that would burn your entire SP bar to deal a devastating attack. However, after this attack the guardian would become dormant, leaving the soldier out of SP for a while (which means out of guardian actions too).
L’Cie ones, though, would be different. Each fal’Cie can offer one eidolon in special so once the pact is done the eidolon is also chosen. As l’Cie you would become very similar to the suggested chocobo knight. You would have a fulltime partner and 2 modes…the one where you both fight and the gestalt mode where you actually mount it to use in combat and for transportation. But I’d like to add another aspect here…similarly to the suggested at summoner chapter, if you have multiples eidolons at field would be awesome having a way to use their “transformerish” style to actually combine in bigger creatures too. If two or more l’Cies summon their eidolons, you would always have the combination option, going from equipment combos (one eidolon transforming into armor or weapon to the other), gestalt combos (they both combining to become a bigger transportation option…just like Shiva and Nix do at FXIII) and colossus combo (they actually becoming part of a bigger eidolon).
And since we talking about FFXIII, the stagger system also would be pretty simple to incorporate here…make the 6 classes from it (turning each role into class…or not)use the SP bar to synchronize with the other classes that can do it (like a ravager can sync with a commander, but not with a warrior) and use the SP bar to emulate the stagger system for a progressive damage boost followed by the stagger effect when the bar is full. At least it’s better having extra classes than adding an extra bar…unless we add the stagger gauge materia so those who want it could equip it. But I prefer classes!