I think the pit lane fire in Monza was the latest proof that this is a meaningful new regulation.
Absolutely, as a pit marshal I support the intention entirely, I also hope it will have the effect of keeping some of the less official "media" peeps out of the pit lane as well (the ones using their phones as cameras

). I'd like to see it enforced in more European series. KK has race overalls which he's used in the pitlane where necessary but sadly they do not meet the ACO's criteria...
I also potentially understand the issue of branding and conflicting sponsorship but finding unbranded Probans is pretty tricky - AWS will do them but at an extra cost. I am also surprised that they don't want to ensure that photographers look different to marshals - I know LM Marshals overalls are very specific but from a distance they are going to look pretty similar, personally in my pit lane I want to be able to easily tell who is who.