Rumor is that Porsche are still doing something that improves their refueling times by a couple of seconds per stop. Which means a gain of about 4-8 seconds per double stint.
Also, it should be noted that as far as development of the sprint and LM kits, though teams can't develop a whole new package without permission (unlikely to be forthcoming) from the ACO, teams can still change parts of them, but that's largely limited to interchangeable parts (dive planes, diffuser flaps if running a wing diffuser, which only Audi ever did, other minor stuff).
Porsche's biggest advantage is that they now know where to aim. This compromising stuff and weather is why all the low downforce rounds IMO should be first, and why adding Monza or Paul Ricard would be a good idea, even if it cost a round, most likely COTA (though I'd probably yank Bahrain due to controversies there, though COTA has been run like a total crap show). Also, the weather tends to be better when Silverstone is a July-August round.