Its common sense that if something is very profitable more and more people are going to want to get into it.
It doesn't take a genius to start mining. Its basically free money. Hence it will become more and more competitive and that will cut into everyones profits.
The next month or so should be very good profits for most. But in 6 months or so, maybe the ones with cheap electricity will be only able to mine.
The only roadblocks I can see are if GPUs get sold out everywhere and that will halt the difficulty jumps but right now there is still massive supply everywhere and even Nvidia cards can mine ETH unlike the Litecoin AMD day.
BTC is a perfect example, its was very profitable during certain times but then everybody wanted a piece of the pie and right now the profits are very very low for most. Only the ones with free electricity make good money with Bitcoin.
I disagree and think it will remain profitable until ETH goes PoS. You cannot compare it with Bitcoin mining, as when the ASICs started, GPUs quickly became obsolete due to the arms race, not because more people got involved. In fact, this caused the opposite to happen as the price of dedicated ASICs started to out-price home miners, the amount of individual miners declined. As long as the Ethereum algorithm remains ASIC resistant, or at least until PoS, it will remain viable to mine.
While it is indeed true that more people will look to bring more GPU's online, this is in itself limited as to how far it can scale. The early ASIC's effectively replaced 10 GPUs, then later on 20, and now 100 or even 1000's in equivalent hashing power. Multiply a large BTC miner today with 100's of such ASICs now and you can see this represents 100's of thousands, or even millions of GPU's worth of hashing power, which would have been impossible to scale to if mining remained in the hands of GPU only.
