The language is definitely different, given the changes to the architecture used for the hardware.
The code was made for a game with a different structure, battle system and space navigation. It wouldn't be of much use.
FFXII is good for what it is, but it feels a lot more of a spinoff than a traditional FF. And as someone who has played FFs from the beginning and seeing it evolve, its identity was kinda defined at that point. And XII would fit as a sub-series, kinda like FFT. In fact, it could be part of its own series with Vagrant Story. FFVIII's magic system permits you to customize your characters with a good versatility. It's not something that you use to attack, but more to determine affinity of your character towards certain elements, and prioritizing certain stats. It's very cool to see how the different party members can be change by using the magic associating with the coherent GFs. The level system is a controversial one, but I find it to have a very good concept. It's broken bc it only looks at Squall's level to determine the enemies' level, when it should take the levels of all party members into consideration. But the idea of a malleable difficulty for the game is awesome, bc the game never becomes too easy, as it is the case with 95% of RPGs once you are leveled up and murder everything in sight to the point of battles being more of a hindrance than a challenge. And every enemy in the game has a weakness to be exploited, so strategy is legit.
The thing that breaks the progression system is also the Cards. The idea of refining them into magic is awesome, but you have access to some powerful cards way too early in the game, which permits the low level run to be an absolute cakewalk. But other than that, the concept is actually smart and engaging. It just needed some minor tweaks.
Oh, and Triple Triad is one of the best card games ever created. That thing is freaking addicting.
At least FFXIII had a good soundtrack.