One proposed answer is that RedBull has made some significant engine gains that require more cooling. The problem with this theory is that the RedBull sidepods have had more than enough volume to increase the cooling in the sidepod, so why take the weight and COG penalty by moving to centerline cooling? The best answer seems to be that they did this because it allows for smaller sidepods and there are enough aero gains to be had by shrinking the sidepods to more than offset the weight and COG penalties.
Another possible answer people are now discussing is that moving more weight much higher up on the car is somehow improving COG and car drivability rather than making it worse. (Yes, and perhaps Redbull has also figured out a way to makes the car faster by increasing the weight of the cooling system rather than making it lighter!) Good luck explaining how all of that is supposed to work. Again, the best, most straightforward, answer seems to be that there are aero gains to be had by shrinking the sidepods.
The next question, then, is how have Redbull managed to shrink the sidepods while keeping the front wheel wake outboard along the length of the car. To me, the answer that makes the most sense is that they're deploying a Mercedes-inspired concept, namely, using a SIS wing fairing to help keep the wheel wake outboard even though the sidepods get smaller.
Evidence in support of this answer:
1.) It makes sense of the rumors (but talk of "zeropods" is a red-herring... it's Mercedes-inspired but it's not zeropods!)
2.) The move to the overbite and shark mouth inlet seem more congenial to the SIS wing fairing concept than the underbite concept they've been using... the overall curved shape (convex top surface and concave bottom surface) of the overbite (with shark mouth inlet) already look a bit like a wing.
3.) The SIS is in a position to turn the outside portion of the overbite and SIS into a SIS wing fairing.
4.) It makes sense of the rumor that the will shorten the length of the inlet.
5.) The move to and shape of the v-radiators in the sidepods appear to allow for the front of the sidepod to taper in significantly enough to allow for enough exposure to form a SIS wing with the outer portion of the overbite and SIS (with a shortened inlet). Their shape also appears to allow the back portion of the sidepod to shrink-wrap down quite a bit to improve clean air downwash, which, if I am right, is the whole point.
My suggestion is that RedBull will shrink their sidepods in a way that preserves their undercut (and its benefits) and also increases the clean air downwash (and its benefits). The placement of the shark mouth inlet will also allow some of the excess pressure at the inlet at high speed to bleed off into the wing and along the side of the sidepod, keeping it out of the clean air flow on the top and bottom of the sidepod. Pure speculation. Can't wait to see if I'm right!