We all know what Training Ground was supposed to do: help new players learn the maps and teach them that quality kills are important. What it actually does is a bit different: a place to go when you're bored, to see what the highest scoring kill you can get is and a place to practice free-running. Only one of the things it does is useful.
Training Ground has so much potential, it could have been what Combat Training is on CoD, but instead it is a flimsy excuse for a practice mode. It could have been a simulator for the real modes, to ACTUALLY prepare you for playing people. We all know that the Introductory Sessions are pretty much like signing the Terms and Agreements of the multiplayer and I think I was one of the few people who while not being super good at Brotherhood actually played stealthy in the Introductory Sessions the FIRST time they played it.
You could have given it settings so that the people would use blend groups and such or they would run around like idiots getting 100 point chase kills (I'd like to call that setting the Anacletos setting) You could have made it useful for experienced players that they could find how to react to roofers or practice spotting their pursuer. You could still make a little playground mode where you could explore the map and practice Free-Running without starting those dreaded chases with the NPC's.
The only problem standing in our way would be the AI, but I know Ubisoft could do it. For roofers just program in the AI for the Borgia carriers, those guys were close to impossible to catch. You already have 'pursuers' in the story mode for Revelations, I don't know if the stalker actually followed you around but still. And if you're on the roof then you can warp the pursuer up there to cut you off, like a smart player would.
As I have said it would be an invaluable resource for everyone, the only problem is getting players into it, which is why you would need an achievement linked to it. It helps with many problemss like new players not knowing what to do so they head up to the roof. More experienced players not knowing how to react when there are players who know how to play stealthy or roofers. It would also help with how difficult it was to learn the maps in Brotherhood.