Already answered on GEA. Essentially:
More SGI than GI (more shovel-ish as said above)
Hot faces on lower lofts
Design COGs to better suit the lower and higher lofts.
Something I didn't think of until now would be to see if it is feasible to offer a flighted shaft option of some type. If the Edel system works as well as Hax says on the GEA and WRX, it's game changing. Cobra is flighting theirs too, but I haven't read much in the way of user results on them.
The shaft tip stiffness is why the shorter 5 iron goes a lot lower for many of us. It's not the 1 MPH reduction in swing speed. Same applies to super high wedges. It's not the 2 MPH more swing speed. After all there are plenty of players who swing their wedges faster than you or me, and they don't balloon. It's all about the shaft tips needing to better match the lofts. We think shaft tipping is all about the head weight, but SL has shown that it doesn't quite work that way.
But, when I tried a softer tip to elevate my SL 6 iron, I hated the way the feel changed. So, I dunno. I assume what is needed is a shaft set that preserves the bending feel throughout the set while having variable tip stiffnesses.