Whether we like it or not, S9s are still very profitable to buy and run. I've been hearing arguments about difficulty increase for a year now. True, the BTC price jumps helped. But until BTC price drops to USD 2500 or the current difficulty triples without any increase in BTC price, S9s will keep running (approx calculations). Focus on getting a good colocation to place your miners or build a colo yourself. Your machines will run for a very long time if you keep colo costs low.

Also, regarding the newer machines that have come/are coming to the market. I'm excited to see competitors, but I really want to get a few hands-on reviews from regular guys like us, before deciding to stop supporting S9s.

Eagerly waiting for the GMO machines...