Unspecialized class ideas

[Shurrikhan]

It would be theoretically possible.

It would even be mildly FF-ish, if you consider adaptive weapons such as Lightning's or Noctis's summoned weapons (or perhaps Cloud's splittable buster sword from Cerberus and Advent Children). But note that these are more components of XIII and XV, specifically. The closest multi-game weapon -- the gunblade -- is not actually adaptive, but merely multi-purpose.

But would it fit the current game? Probably not. This is the direction that 1.x was going into, whereby each weapon had abilities that come most naturally to that weapon and could be acquired therefrom but could then be used on any other. Rather than allowing for meaningful synergies between them, however, Yoshida let the open-arsenal system rot and then replaced it in entirety with 2-3 weaponskills (or, weaponskill combos, though usable only in a specific order and therefore offering no more than 2 options for one's first combo, if that) per class/job while removing cross-class weaponskills. What we have now descends from that decision to pare back options to a bare minimum and then improve from there -- divorced from virtually all sandbox elements.

The closest you're likely to come to The King's Avatar now would be a Weaponmaster job with a seemingly larger than standard toolkit size, provided it can be made with nearly the same ostensible depth as Ye Xiu's.