This feat, phrased as is, wouldn't stack with either a monk's or a barbarian's Unarmored Defense. It would give you the option of using this formula instead of the class feature's formula.As written, monks could use that to apply three stats to AC. Monks are MAD, so it's unlikely to be a large bonus, but it could be. I heard barbarians can apply Con to AC, but I've not seen one in play, so I'm not sure.
4e had this same feat, but forgot to make it a bonus feat for monks and avengers (who essentially had this as a class ability), so you could double dip that way.
In general I don't like the idea, because the numerical bonus is too "soft". Max +5, minimum ??? I think monks should drop the Wisdom bonus to AC and just start with a higher bonus instead.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.