Amazon has the resources to make themselves a viable 3rd and unique option.
If they run the console the way they run their business, then all they do is reinvest. And depending on what their ultimate goal is, (which I believe is not to generate a huge war chest since I don't believe Amazon reports in profits they sit on, but profits they throw right back into the business.) I'm sure they will eventually build an ecosystem of service & product for exchange that will shame even Apple and iTunes.
What other products does Amazon currently invest in that would merge with their Console/Tablet/TV connected take over? They never want you to leave your couch/house again. They will literally bring you everything you need through the use of a few devices. Console connected to the TV, Tablet in your hands, phone in your pocket. Games, food, toilet paper, clothes, more games, TV, Movies, more toilet paper...
Amazon is a major distributor of physical goods, and give incentive to 3rd parties through sales and promotion on Amazon.com in exchange for timed/exclusives and extra goodies/exclusive DLC. They could pull lots of leverage with 3rd parties WW as Amazon is pretty popular everywhere (except Japan, and that's only because of their strict nationalisms, but even there they still do alright.) and if they can double down on distribution through digital efforts... oh man. They already have all the infrastructure in place.
Amazon would be a very interesting choice for a major 3rd competitor in place of MS.
Sega would never be in such a position of opportunity again in such a short time. Their 3rd party output isn't even good enough to sell other peoples hardware, so I doubt they would be able to sell their own. Their best bet is to sell themselves to Nintendo and ride that wave till it crashes into the rocks, because that will be as close to the glory days as they get in a long long time.
No offense to Sega, but they just don't have it anymore... but together with Nintendo they could both become something more. something better.