I think it's amazon , the world's largest online retailer. The company was originally a book seller but has expanded to sell a wide variety of consumer goods and digital media as well as its own electronic devices, such as the Kindle e-book reader, Kindle Fire tablet and Fire TV, a streaming media adapter. Accepting Bitcoin really is a next big move of them.
In my opinion, since Amazon is an online retailer. This is 30% possible, 70% not and it's is still related to the volatility of cryptocurrencies especially if it will be intended to use as payment. There are tons of things that needs to be considered particularly the following:
If Amazon third-party sellers are willing to embrace it
Purchasable products in Amazon website will become cheaper or overprice at no time.
Profitability of the entire Amazon community will become unstable (Unless they're willing to hold their BTCs until their preferred time of conversion to fiat)
Even if Amazon will come up with a system that will automatically update everytime there's a movement happen with BTC in exchange. It is still risky for a well - established business in Amazon and I'm sure 90% of them will not take that risk.
Anyway, it's still only my opinion. Let just wait and see how Amazon will integrate crypto to their Marketplace, IF IT WILL GONNA HAPPEN
