May I remind you of something called "HALVING" before going crazy on a purchasing spree?
That is a million years away. By the time halving arrives, each and every S7 will have long been tossed in the bin. Miner lifetime is far shorter than that.
my Sp20 is still very profitable at $0.1/kwh after ~9 mo
My Sp30 is still profitable even without downclock after 11mo
Conclusion: difficulty rises in the last 10-12 mo were moderate, allowing good hardware to function longer