GB:
Short answer.
This is a "sketch". There is no business plan attached. It is an idea. Someone received their degree for thinking outside the dreaded "box".
You should encourage this thinking, particularly since you are not yet a planner, a mayor, a premier or anyone else who really doesn't give a shit.
The latest half-assed (also without a real budget or business plan) idea is just that... the latest. So you've hopped on that wagon, good for you. How opportunistic.
Gardiner schemes come and go. I've seen six of them that had a (fiction) business plan.
My point for one last time is.... it's worth a look. You are incorrect about the economics, you are incorrect about your vague notion that the engineering principles are not sound (cantilever cable-stayed construction IS often chosen because of the way it mitigates distruption), and you haven't explained your opposition to this in any but an elitist, I'm a know-it-all way.
I don't think this has a chance in hell in this city, however the simple fact that it addresses the issue of "minimal disruption" was enough for me to overlook the flaws and problems and try and see if there was any merit to the idea.
Meet me in the alley behind Sam's at 9 pm... knives, not chains.
P.S. forgot to mention you don't want to hear the long answer.