It is so difficult to talk about this kind of things in internet without offending anyone or being understood..., it is all so complex. But I am going to dare to give my views.
For a start, to me this turban is not like other turbans, for example the mentioned Hollywood glamour ones. Otherwise the blacklash would have happened before as Gucci has lead the revival of the turban and has been offering several models every season since de Michele arrived... as have many other brands, I myself wear Missoni turbans in the beach and I think the associations they trigger nowadays are different from this particular turban. While it is true that Eastern influence and fashions was often, not always, behind, turbans have been worn as headwear now in Europe for centuries. Think Vermeer de Delft. And before that of course Spain, Greece and parts of Italy were under various Muslim/Ottoman rules and this type of head wear standard. In the first part of the XXth century the fabric turban was the working girl cheap alternative to the hat in a continent wrecked by poverty. So there are so many associations I do not think of it as cultural appropriation and yes, my perspective is that of a ‘white’ European (even if many in my family are darker that most Indian Sikhs, being as we are from exactly the same indo-caucasian stock).
Now, this particular Gucci turban is different because it is basically a faithful (if mock) interpretation of the exact turban that is nowadays worn by Sikhs, a religious minority of India, and which therefore has strong identitary and religious connotations. Gucci should have been more careful and aware. Does this mean the use of the turban in a fashion show (which happened months ago) is offensive? That is for Sikhs to say.
And offensive as it may be, I don’t think it has anything to do with the blackface scandal. There it was not about the appropriation of an identity or religious symbol. It was about the frivolization of a symbol of oppression that recalls one of the most terrible things a group of humans have inflicted on another. That is not cultural appropriation.
Cultural appropriation in a religious context as with the Sikh turban, can be tricky and should be avoided, But in my personal opinion, in other cases it goes too far. What is cultural appropriation and what is cultural cross fertilization? Stella McCartney got a blacklash for using African wax print fabrics. These fabrics (which were incidentally introduced in Africa by the Dutch) are exceptionally beautiful, why not spreading their use? In the meantime, traditional wax print factories are disappearing fast in Africa, the know how lost with them, while cheap t-shirts and jeans are literally dumped by the ton on the continent everyday. Is that really preferable? I find behind many a cultural appropriation debate there is an underlying sense of white supremacy which results in guilt driven paternalism. Like with the ‘Asian and Hermes’ thread in this forum, which makes some white people uncomfortable while Asians happily contribute and enjoy it. From the kimono to the sari or the kurta, passing through the Native American moccasins or the Persian kaftan, everything we wear is imbedded in a myriad of cultural influences and to me, those influences are to be nurtured and encouraged and more desirable than the imposition of western wear on everybody else...
Nick is no Sikh, but he and his fashion minions have suffered no indignant uproar. He has stated he doesn't even believe in religion. Nick Cannon: “I’ve been studying the Sikh faith. It didn’t start as a fashion statement but it kind of turned into one.” All rightey then, you do you, Nick 
