I wish we had this to be honest.

Hate me all you want.
But in FFXI i had a blast equipping whatever weapon i want. That Naginata Polearm was so dope on Samurai for Bird parties, until you got Amanomurakumo!
And i wish so much, that we could use a Naginata on Samurai, additionally - not instead - to the Katana.

I don't think Balancing would even be an issue, just make them the same stats really.
It's more of a... "okay, now we need to make new stance/auto-attack animations, possibly new skill animation that detect which weapon type you have equipped,
and if you want them to be seperate and have one of each for every primal etc., then it's instantly twice as much art design work.

What.. I could see them actually implement, is weapon glamours that are unique weapons. But making this work with current animations might be tricky or limiting too.