The system can work, in other games, but I think a lot of people have already said why it wouldn't be that good for here unless we were seeing some maaajor changes to the game (in order to properly facilitate whole new skill system and tangibly interesting choices).

With that said, for fun, I'm sure we could imagine a job that might do this. Like taking the FFXV swords, axes, shields, etc, flying and floating about, you might be able to wield many spiritual weapons and changing your main weapon would shift some of your kit around. Noctis the job lol. Fun part of that is it could theoretically be any role you wanted to design it for, as it'd be a mostly physical. non-elemental, psychic based motif with loads of weapons to call art from.

Or maybe they might make it FFXIV's Onion Knight, as a limited job, literally get to slot in different weapons (that then 'literally' show up in your spell arts). Switching to different main weapon causes you to switch to different set of skills, while 'background' skills are based on the entirety of your selection (so some skills are determined by your loadout in general and some are determined by which weapon you're 'maining' at that time). To make stacking and diversifying interesting might see a formula on weapon diversity such that you might get more powerful abilities if you stacked more weapons of a certain stat type but that the stats have a progressively ramped stat benefit such that the difference of 1 to 500 is not the same as 500 to 1000 and so having a high stat diversity may be seen as advantageous (while also granting a greater diversity of skills, almost like classic sub job systems), yet also having high stat stack unlocking deeper tier abilities on that stacked role would it's own advantages too.