You make a great point. I agree, it depends on how far into the future you are talking about and a bunch of other variables too. If bitcoin is ~ $200 next week and you offered me the 8 board complete kit for $1200 at that time, I would definitely buy the kit. But if bitcoin is $600 in 4 weeks and you offered me the kit for $1200 at that time, I wouldn't want it.
Huh? Your logic is all backward. Why would you jump at buying a miner for 6 BTC and turn it down for 2 BTC?
Because at that price everybody and their mother would want to mine and difficulty would go through the roof before any chance to ROI.