Air NZ has a system like this, and I think there's another FFP in the world which has also just implemented this kind of change.
Air NZ Airpoints, in fact, allows Gold Elites to bank "excess" status points over a certain threshhold (and these carry over to the next year). When you reach another threshhold, you get another year of Gold Elite status in "reserve", to be called upon when you cannot normally sustain your Gold Elite status. And you can bank multiple years of these Gold Elite in "reserve".
There's quite a lot to be had after Platinum qualification itself. Other people may not choose to enjoy this (i.e. go for 2,400 SC rewards). But the fact that rewards beyond 2,400 SCs exist is probably the compensation for not having a "carry over" system.
For lower ranked elites, is it worth offering this........ what would be the implications, even if, say, your "excess" SCs were carried over at even only half the amount? (For example, if you had 120 SCs more than your last status threshhold, next year you'll carry over 60 SCs)
I wouldn't mind having a new 2,400 SC benefit where you start the next year with 600 SC (i.e. half of Platinum requalification, with these 600 SC also counting towards the "QF metal" requirement for P1).