Punk, though fashionable in Britain from the late 70s, only really caught on in the early 80s in Europe, if at all.
That's not true, there were punk bands in Belgium from the mid 70s onwards, as well as other European countries such as Germany and France. Lots of British punk bands used to go there to play. Of course, there were still hippies about but punk was a rejection of the long hair, flares and 20, minute guitar solos and the fashions quickly caught on in Europe. Anyone remember Plastic Bertrand and "Ça plane pour moi"?
Hergé was still working on the book up until he died in 1983, or so it is said. I just thought that if he'd drawn the art crowd looking like in those sketches it would have looked rather out of date in the mid 1980s. Of course we'll never know what the final book would have looked like. Perhaps he might have given Tintin a mohican? ;-)
As far as Haddock goes, I think Hergé was floating several ideas; that Haddock would hang out with arty types; change all the decor in Marlinspike to a contemporary style; experiment with his outward appearance and persona, etc. I think one of them was for Haddock to smoke dope. I really don't believe any of them was intended to make the final book, rather they were a list of spontaneous ideas from brainstorming. It gives you something of an insight to Hergé's working methods.