The current forecasts don't predict cost parity for the next few years. I wouldn't speculate as far out as ten.

What you'll see is that spinning rust will increasingly become used for cold(er) storage due to still offering cheaper bytes, and (relatively) ever increasing cost of IO (you get one spindle per il unit, but at increasing capacity, with barely a change in sequential throughout and no improvement in random access). This is happening in data centers now, either through explicit product tiring or clever offloading.