I’m very against this idea, but regardless of this opinion and thoughts of how it would take away all weight regarding class decisions (a lot of this has been removed with the new system, but this is for the best), keep in mind that there is also a stat system involved with this game. Any kind of class respec would also involve a stat reset, which already exists (for testing purposes, yes yes, but 90% sure it’ll be a cashshop item at some point). This would just be an additional price and also hiccup in the system, making it quite clumsy in the current system.
A FFXIV “weapon = job” system would also not work due to stats, but also due to weapons having cross-over usage for classes.