tanabe is coming out with the Seven series because they are trying to IMPROVE their lineup.
the seven is gonna have electronic dampening control that can be preset and adjusts on the fly depending on speed.
also, the valving of the suspension is totally different than what the DD was.
on other brands of coilovers (specifically the "cheap" 32 way adjustable coilovers), they promise 32 way adjustment but don't pack as much punch as the sevens will. the shock dyno chart above shows the seven (in red) versus another brand on the market (in green).
an analogy is that with the other brand its like getting 50 cents in pennies
while with the sevens you get a dollar in nickels.
the sevens will not be a "drift" or "grip" coilover, but will have a broad range from hard to soft, much greater than the other coilovers on the market. therefore, you won't be limited to your type of driving whether it be track one day and the next minute driving home with comfort.
the spring rates will be 10/8kg and 12/10kg. still kyb obviously, so they aren't downgrading their materials or production methods.
and the reason why many companies are coming out with new things (many of them with more "affordable" options) is because the current market does not support the high quality stuff. that's a whole 'nother discussion though.