We already support universal apps, and if there is anything we need to change to support the Xbox One then we will obviously do that as soon as humanly possible.
As for Spartan I've heard it has performance improvements, so it should be a nice improvement over IE11 - but I don't think they have any plans to port it to windows 7/8 right now, so the ridiculous OS support limitations of IE will continue... even if Spartan is as good as Chrome, I'd still recommend Chrome or Firefox simply because you can get the latest version on any OS!