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There was a remixed New Years' project that was featured a year or two ago. I seem to recall that there was a lot of controversy in it being featured, because many Scratchers felt that the original creator deserved the recognition more. Thankfully, in that specific case, the original creator seemed to be okay with the fact that a remix was featured.

I think this could explain why remixes are rarely featured — in general perhaps it's best to give this recognition to the original creator of the project.

Trending is also probably similar, although it's a little different because that is done algorithmically. My guess is that Scratchers who see a remix of the project would probably want to see the original project.