Making a bigger DRS opening would be fairly common sense stuff, but obviously Ferrari aren't doing this, probably cuz you still need have the whole package work efficiently when the flap is open, and I'm guessing the Ferrari in its current state would not with such a simplistic change.
I get the impression that Red Bull looked at how DRS zones exist on basically every damn straight on the calendar nowadays and genuinely built their package to work especially well with DRS open. It gives a qualifying advantage, and it gives an overtaking advantage in the race. The harder part is probably ensuring that the overall car still has great downforce when the DRS flap is closed, and well....that's why you have Adrian Newey.
But yea, I wouldn't be surprised that in the case of the FIA not showing any signs of cutting back DRS usage next year thanks to the effectiveness of the new regulations, more teams will look at trying to exploit this design strategy as well for next year's cars. It might be too late for Ferrari this year, though. Sure, there's lots of room for molding the sidepods from what they are now and all, but going away from what's likely a quite developed overall package to something quite different probably wouldn't lead to better results.