I just thought of this idea randomly while waiting for my Footman to level up so I could turn him into an archer. While I was waiting I thought it would be cool if you could be able to build something like a target dummy for Footman to train at. You could also be able to build something like that a blocking machine for Knights and a target to shoot at for Archers. To make things harder maybe these could have a chance of breaking, meaning that using it won’t give you XP so one of your workers would have to repair or replace it. This could be helpful in survival mode where everything is harder.
For decoration I think that’s a good idea, but not to gain exp. It it already easy enough to level up your military, especially “late game” (It begins fairly early already). I think Furniture Expansion Pack has the dummy deco, though cannot be used by the military. It would be interesting if they would interact with a dummy, though.
Perhaps training at dummies could give different perks all together? Like footmen get faster at attacking and knights can block hits better.
Or it could give a happiness boost for something like “I feel like I’m getting better! I feel that can protect the town against any threat.”
Even then, I think I training dummy would be a nice thing for idling/patrolling.