Have not bought any of the current and I do not intend to unless prices come down for equipment and the energy use comes down to. Maybe in the future after halving some massive improvements come to the asic world and provide a lot more effective units.
The current S7 price is great, asking for cheaper would be a bit wishful thinking. At the moment i would ROI one in 4 months, that is pretty great. Having even more efficient hardware would not make mining more profitable at all.
If they come up with 0.01J/GH unit, then everyone will have those, and your profit/watt will be about the same as now.
Right now, the Avalon6 is a great unit, but the price is not keeping up, so this show that you can't really expect things to suddenly be super cheap, affordable and great return for you
but not be for big operations that pay 10 time less for electricity than you and get cheaper deployment cost/GH than you.
Your btc profitability is pretty much forever locked to a range, based on your electricity rate/what deal for cheap hosting you can find.