IMHO, while the majority of mining is still carried out by non-corporate sponsored miners, then the base motivation for mining will be driven from a passion for this game - and the great carrot of making money while doing pretty much nothing, rather than, being driven from a pure economic sense, so things like ROI, GH per watt etc are really an exercise in academia for most, or a talking point for the depressed who are watching their BTC per day drop, or even used as an attempt to discourage other miners from expanding their rigs, while expanding your own rig...that sort of thing.
The only ones really strictly budgeting out their BTC based on those factors are those with millions invested in this game, for the rest of us, we will just keep coming up with reasons to keep our, USB miners, 400w over clocked antminers etc, running even when they are running at a loss, we will down clock them, down volt them, turn them into space heaters, fry an egg on them, use them as 400w xmas lights, whatever, while at the same time, any new player wanting to get into mining will have the "theres no money in mining, BUY BTC" mantra yodelled at them, meanwhile the same yodellers are probably still sending every mBTC they have to BITMAIN for more space heating egg fryers
If the difficulty was to ever fall in a 14 day round, many would celebrate by adding another 10 TH/s or to their rigs, thus making sure the drop would be a one off, and most certainly continuing the rising difficulty madness
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