BlackIsland:
had Haddock made a radical transformation, I wonder how it would have sat with fans
I'm not sure that I'd have worried; I don't imagine that Hergé was considering it a permanent alteration to the Captain, just one of his many passing fancies, like his spell as a monocled country gentleman.
If there had been more comic mileage in it, he might have carried it across into another book, but just as likely the Captain would have cast his eye about, and come up with some new hobby to pursue or lifestyle to try.
In regard to how dated or not the idea of Haddock as a hippie would have been, well it could be just a facet of the length of time over which the book develped - and the fact that development probaby ground to a halt pretty much around 1978 or 79 - so Hergé might have been forgiven for not putting punks in. And Punk was only one "tribe" at the time - there was also a Mod revival (Two-Tone, ska, etc.) and a Fifties thing too (Rocky Sharpe, Darts, Flash Cadillac etc.), plus the ongoing success of disco, rock and what have you. Punk may be the one which the "cool" rock press and their disciples wanted to promote, but the charts were far more diverse.
Even Plastic Bertrand was not what he seemed, as although he's a classically trained composer and musician, who studied at a conservatory, he wasn't actually
on the record of
Ça plane pour moi - it was recorded and sung by its author Lou Deprijck, who then provided the vocals for Bertrand's next four albums.
A long-running legal dispute has followed, with a court ruling that - in spite of not being involved at the outset - Plastic Bertrand, not Deprijck, had a right to claim to be the song's "artist"; this decision was later overturned.
I did once read that Deprijck may have written
Ça plane pour moi as an anti-Punk joke, to show that a really bad song, sung badly, could fool a Punk audience into thinking it was somehow good, but I haven't been able to find a reference for this, so take it with a grain of salt.
Anyway, after that meandering aside, getting back to Haddock's hippie phase, I might also suggest that we consider that the change in many ways was echoing Hergé's own changing taste - he, like the Capitain, underwent a move away from the tailored English suits and upper-middle class art circles, to being more casual and moving with a more Bohemian set, as well as opening up to popular music from groups such as Pink Floyd, and perhaps dabbling in drugs.
It's not beyond credibility that he was self-aware enough to see that while this lifestyle change might have been new to him, he could still be being held to be an out-of-touch oldie to the truly young, and that the circles which he moved in were in many ways as ridiculous as the stuffy bourgeoise life he thought he was leaving. Haddock's fish-out-of-water exploration of the "in crowd" could have been a mirror to his own, exposing his own foibles to ridicule as he had done before.