Well this makes sense, to a certain degree. For example , in the long haul, I may mine with K16 for 4 months until it costs more to power, then to mine.
Then I would replace said HW with "better" HW in theory, as 4 months from now Bitfury and others will have more HW in the market.
It may get complex and separate calculations may work better though
One way to handle this would be to require multiple calculations to be ran but add a variable of "wait x days first"
Tbis way you could run the initial hardware calculation for the first set of hardware. then Do another one saying wait 120 days then calculate for 120 days. So it still adds up difficulty but just doesnt factor in mining for the first period.