I wonder when there will be a market S4 and S5? 
Cloud mining is a method of selling away old end-of-life hardware as GH so I wouldn't expect fresh hardware to be sold as cloud GH anytime soon, except maybe for sky-high prices.
Farm owners want to milk the highest profits from new hardware for themselves, that's for sure.
Although this is true with most providers I feel its a little diff for bitmain. The S2 and S3 are still somewhat profitable and was produced in bulk which is why they offer cloudmining for them. The S4 is still selling a lot and I am sure is not as heavily stocked as the S2s and S3s. Remember when the S1 became unprofitable they converted the shares to S2s essentially. Most companies would just terminate the shares because thats what it says in the website. S5 isnt even out yet so doubt we will see it on hashnest for a long time.