I don't really see the value in this other than the nostalgia factor. But personally, I wouldn't want to add additional risk with no reward to any former-level-cap BC. It's not going to make anyone hang out in new places, either. People gather around the most popular content. A few people going on a retro nostalgia trip isn't going to influence that.

As mentioned above, monstrosity does a good job of that considering there's a huge number of monsters to play with, you can keep going back to old areas many times.