Why would Chinese owners want to buy that? It seems unlikely that Australia will hold its bargain for the whole 200 years given current political climate.
This just seems like a really bad deal for whoever buys it.
Regarding your 10% assumption: In June 2014, the Adelaide Advertiser reported that SA Power Networks made after-tax profits of $420 a year from each customer compared with $92 for another Li Ka-shing-owned utility in Britain. I don't believe the average customer paid $4,200 for energy in 2014, so their profit margin must be much higher than 10%.