The content has yet to be released in anything but a few screenshots.
It was actually released in Thursday's snapshot, so you can test its functionality.
I think it should probably be restricted to rogues, just because they are the sneaky group, but it really doesn't matter overall which classes get it. Warriors and Rogues are melee classes, so they pretty much have to have a sword (or alternative weapon) in hand to do anything. Warriors also are heavily reliant on armor. Holding a sword (or any tool) and/or wearing armor totally defeats the purpose of the invisibility potion because they can still be seen. Thus, the only way to be stealthy with the invisibility potion is by going somewhere completely unarmed. You could get into a town this way, but you couldn't kill anyone because they could see you. It would be an effective stealth-raiding tool, but nothing really beyond that.
I would personally not like the idea of it being given to Casters and some Healer specs though, because they don't really rely on tools and armor that much. A Disciple can do a lot of damage with just a fist (which is invisible), and a Caster who manages to get a legal keybind mod could wreak havoc with an invisibility potion. Also, some Caster specs have the ability to teleport their friends to their location, which, if used with the invisibility potion, could quite reasonably be called OP.
I also think that, if it were added, Recall should be unable to be used while invisible. While only one person could benefit from a Recall (with the exception of some Caster specs), it could still allow them to do massive damage to a town's resources effectively invincibly.
Actually, I suggest that skills be completely unusable (except maybe for Rogue classes) while invisible. This would make the potion only useful for basically nonviolent covert raiding, because carrying weapons and wearing armor would give someone away immediately. The only maverick there is the disciple because their weapon is their fist. I'm not quite sure how you would get around that.
Also, why are we discussing invisibility potions in this thread?