A month back i have seen people saying that s9 will turn into a junk box very soon....
but their own views have been changed by now... Its mainly due to hike in the price of BITCOIN that demand of s9 has increased and people are again demanding antminer s9.
Presently 517$ profit is observed monthly...
But how long this profit will remain as it is... is the question of the hour.
What i think is antminers should not be considered giving the same profit always... it is because their profit totally depends on the rate of the particular coin they are mining.
Secondly, apart from rate... difficulty level 9s one of the concern for sure. But due to the fluctuation of difficulty level in mining.. this factor also keeps on changing.
SO ultimately it can be said that antminer's future is not very much predictable but their profit will surely remain in benefit always. Its because even if s9 does not mine very much in future monthly but the hike in the price of bitcoin can definitly change your wallet value where u will keep adding your bitcoin.
so its very important that u sell your coin only when its most profitable... and KEEP ON MINING :)