Most likely not S-duct related, but they have brought new (presumably higher-cooling) bodywork to Bahrain, they just did a second shakedown before the test and posted a video on Twitter (as you can guess by the horrendous compression).
As you can see, they have a giant slot that goes all the way from the halo height and blends into the regular louvres on the sidepods. Very elegant. Weird that there are only two slots (highlighted in yellow), but perhaps this is adjustable based on demand.
On a slightly more tinfoil-hat note, they also posted a bunch of pictures with dialed-up contrast which conveniently hide the front of the sidepod and floor entry where any S-duct inlet could be located. And these new slots (the front one at least) could very well be hiding an outlet.
I agree with the above statement that it would cause a stir for them to turn up with one since Ferrari did, but any
alleged flow of information presumably goes both ways. Who’s to say someone at Haas didn’t think of it first?
Hypothetically speaking, of course.
"You can't argue with stupid people, they will drag you down to their level and beat you with experience"
- Mark Twain