Aside from the contemporary points mentioned in that article:

Is the future of hate multicultural?

I understand why articles like to write that way, but it has been for a long time.

Not exactly equivalent but insightful: The leadership of both the American Nazi Party and Nation of Islam (Black supremacist) saw each other as allies with compatible goals of racial separation. The attached image is from a Nation of Islam summit in 1961, where the person in the center of this image spoke on stage in (overall) praise of NoI. There are many articles about this, an interesting read.

And as for multi-racial racism, of course. Many see some races as alright or tolerable and others as beneath them, a big example being anti-Jew conspiracies, anti-Muslim sentiments in the West after 9/11, and anti-White sentiments especially among the many nations affected by colonialism. Sometimes racism isn’t explicitly based on supremacy of one race, and so I firmly believe we will see lots of people of different races join up with groups dominated by white nationalism, even if they don’t support WN themselves.