isn't it safe to say that mining with 28nm even as early as February wouldn't make ROI?
For some retail machines you might be right.
Cost of equipment is key. We should be selling budget machines with our 55nm chip and they will ROI because despite being 55nm they will be cheap and they will be very very good custom-build chips. At the GH/W level they will be 65% of the Q2 20nm KnC Neptune.
https://coinplorer.com/HardwareHow do you figure they will be 65% of a Neptune in GH/s/W? KnC says they're plan to come in at 30% less than their 28nm products, so 0.7J/GH at the wall. These 55nm chips are slated to come in at 1.32J/GH at the chip level (Antminer is 1.3J/GH at the chip), and will likely come in close to 2J/GH at the wall. That's 2.8x more power than a Neptune based on estimated specs.