To make a long story short also since new rapid transit lines spurs development around the lines then why not charge them something, but treat it more like a co-operation to compliment each other particularly with station building and what's integrated into it. This particular method may very well have merit, especially since there's a chance to see how it'll work out with this London line.
So are you thinking of a one-time fee, or a recurring tax? Both methods have their merits, and their drawbacks. I'm just curious which one you see more fit for this type of scenario.