I think the temperature at that altitude is ideal for mining (It also bears the risk of the equipment freezing!). Now if only we could stick together a couple of S9's and hook them up to a little solar power generator in there... That would be even more amazing!
Hook it on what?
Temperature in space close to Earth is around 10 Celsius, there is no risk of freezing and without air there is actually no air convection and heat is lost through radiation....it gets complicated.
But that balloon was flying in the stratosphere and at those levels the average is -20-10 C.
Can these balloons stay up there indefinitely or do they return back to earth? I know there are projects like this to provide internet to remote regions. Project Loon. 
At maximum a month. Depends on the size, the cargo...
All that today seems to us useless and unreal tomorrow will be quite common. I think and mining in space is quite a real activity in the near future.
By the time we would be able to launch "something" that can power up 60 ThW of miners the reward will be 1 satoshi
.Using solar power to mine bitcoins on space with some avialable for now asic devices interesting idea, but can it ROI space shuttle ?
Just the launch of a Falcon X is around 6000 BTC. Of course it's not viable.