I'd be surprised to see recognized companies like eBay or Amazon launching an alternative version on the darknet that would accept Bitcoin or privacy-oriented coins like Monero or Grin. This seems more like a dream than anything else, considering that the darknet has a lot of bad reputation. But in crypto land, anything could happen. If there's demand from people in the mainstream world into marketplaces which rely on alternative networks, then we'll be able to see more legitimate services over time. Otherwise, marketplaces using the clearnet (public Internet) will still be the norm of e-commerce.
So your gist is that you want to do fully legitimate transactions on the darknet? Such as buying your weekly groceries? I thought you meant legitimate in the sense of dodgy site least likely to rape you.
Erm, why?
No one's ever going to bother setting up a market on there for any reason other than avoiding the law. I've had a fiddle with Tor and it was so slow I nearly passed away. If 0.1% of customers will consider a crypto transaction on the open internet maybe 0.00000000001% would try the darknet alternative.