It really depends on how far the bluff goes. The only caveat to the 407's insane return on investment for those folks is the Government finally finding a way to claw it back. People have long speculated on how, but this might be Ford donning the Trump hat. A 401 tunnel is just one more thing making the 407 slightly more redundant; we are planning a Transitway along it, the 413 cuts into traffic on the western half, and now this.
Now, credit where due... Would I buy news headlines for these things as a fund manager? No. But if an EA were to be completed, and the 413 just happens to be u/c at the time, it would be negligent of me to not at least check the numbers again.
Ford only really needs to make this seem like a better alternative to some drawn-out legal fiasco he's willing to initiate. That would cost the 407's owners time, money, and scariest of all, possibly the entire highway without compensation. To call that sort of bluff, you would actually have to risk entering the courts.