Shouldn't be hard to implement something like that, they have the training dummies in places like the Gladiator and Pugilist guilds already. Could easily set up an NPC that stands next to a training dummy in each of the cities. Talking to them lets you set up a special instanced area allowing you to spawn a training dummy in the area. It doesn't move, doesn't do anything but stand there. You're instantly given full MP/TP while in this instance to practice as many moves/spells as you want. Leaving the instanced area removes the effect. If in a party you can teleport everyone into the instance to practice on a single or multiple targets.

The dummies themselves would be impervious to death like the floating eyes in Dzemael Darkhold allowing you to wail on them endlessly.