Microsoft has confirmed that Xbox One controllers, as well as other accessories for the present console, will work on the upcoming Project Scarlett.
As to whether or not ALL accessories for the Xbox One will be functional on the next-gen console or which accessories they are, we can't be sure just yet. But Xbox One users can rest assured that their current controllers will work on the new system, which is due for release next year.
Eurogamer sought some clarification on the matter and have since heard back from Microsoft but their statement didn't do much to remove the shroud of uncertainty over the accessories bit. They did confirm, however, that the next-gen badboy will be able to play games from across "four console generations" and that players will be able to take their progress with them whenever they upgrade.
"During the Xbox E3 Briefing, we announced that thousands of games across four console generations will look and play best on Project Scarlett," the statement from Microsoft reads. "We also continue our commitment to compatibility by ensuring your Xbox One gaming accessories and Xbox career will also move forward with you. We have nothing further to share at this time."
Since then, Microsoft's Larry Hyrb and Elliot Hsu have told Geoffrey Keighley's YouTube Live at E3 show that the Xbox Elite controller 2, which was recently announced, will work on Project Scarlett. That in itself is a relief when you consider it costs $180.
There are still questions regarding the other accessories though. Microsoft hasn't told us what they will be exactly and it's way too risky to assume that all of them will be compatible with Project Scarlett.
Despite their brilliant E3 presentation, the company has left us somewhat in the dark over this. Plus the absolute blank on the next Fable, which has more or less been confirmed to be in the works, has come as another disappointment.
You could read up on why the game wasn't mentioned at E3 here, by the way.