I don't know if this is a good idea or not....but
Assuming, as the reports state, they are looking to sell 60% of it then their annual dividend would drop to about $115MM....in perpetuity. So they will see a reduction in their income from $289MM to that amount. So the cost of this $10B would be about 2% a year which is roughly what the government of Ontario pays in the bond market today for borrowed funds. So, economically, it seems pretty neutral.
I understand your 10 year calc but assuming they build a bunch of transit with this (as is the plan) and since we have yet to see any transit in Ontario that does not need some sort of subsidy...I wonder if in year 11 if that lost revenue is looked at differently when the cash needs of the province are higher but the income is lower?
The province seems to be saying that they would only sell a part of the utility if they could maintain control of pricing.....so I also wonder how deep the market will be for a $10B equity investment with so little control of income/profits.