I dunno. On the other hand it's really not all that amazing?
Sure, but that's the case with a lot of stuff we made innate, like innate Monster Skill, innate Float, innate Train, innate Any Weather, innate Move on Lava. It'd be more to stick it on there, and have someone forget about it, then 5 hours later suddenly go "oh, hey, I could Equip Change in this situation".
Chemist'd be the obvious one? Class doesn't need it, but it'd be a neat gimme for a class that's otherwise pretty much unchanged; plus stone gun is one of its best applications.
Theme-wise, there's something appropriate in my mind about sword users changing weapons (the Gilgamesh/Advent Children Cloud effect); so, Knight or Geo? ORLANDU?? Hell, all the NPC swordspeople?
Alternately, if we understand it to be choosing a different arrow, Archers would benefit from being able to switch status effects/elements, crossbow/longbow, draw/sheathe shields etc. Mechanically this might be relatively useful (though still not particularly noteworthy, obviously). Equip Gun Stone Gun Archer would be the best ever, too.
Bonus points if Equip Change could be made to count as wait for CT purposes (if not the full 50 CT NEB suggested). I'd really dig that. Or if it came with the Defend status.