This all boils down to value.
The Xbox One didn't ultimately fail because of power - the system has some gorgeous looking exclusives for it like Ryse, Sunset Overdrive, and Quantum break. And ultimately, the best selling PS4 games aren't really graphical juggernauts (Destiny, CoD).
Failed messaging, the combination of weaker hardware at a higher price, and a more aggressive competitor ultimately ended up driving the story of this generation.
The prospect of a 6TB Xbox 2 is interesting, but it doesn't come without a cost. They will need to match some pretty substantial upgrades for all areas of the console (power supplies, memory, cpu, etc).
Would a $499 Xbox 2 @ 5-6TF succeed against a $399 PS4K @ 4.2TF? I think at best, it would slightly re-engage the US Xbox audience, but I don't think it would have them sway sides. It may put them at a competitive disadvantage due to price, more than anything.