@bertybassett I totally agree, but with say $700 a coin where is that end of profitability?
Just an example, say you are running 1PB of space, that is about 72 drives with 14TB, which will fit into 2 cases 4u with 36 cages each. 72 drives at 6W power plus the processor and other stuff around it costs you to be conservative 20 kWh per day. If you have cheap electricity that will cost you about 2$ per day. The investment cost, repair cost, maintenance cost, and ROI is neglected here for simplicity.
So with 1PB space, network at 18 EiB today, the income at the moment is 0.5 XCH per day, say about 350$ per day at $700 per coin.
If you turn this around, the network can still grow about 175 times until 3150 EiB = 3.1 ZiB for a rig like this to be profitable in terms of electricity (not investment cost)
So from my point of view 20 EiB will not be the end of this game if the exchange rate XCH stays as it is or increases.
Another endpoint is the value of XCH, if that were at 4$ per coin the 1PB installation would be at break even in terms of electricity cost.