I've been an XNA.DirectX MVP for 6 years and I don't see any signs at all. If Microsoft is working on such an API they have either managed to keep it amazingly secret or they have not started work on it yet - in which case don't expect to see anything anytime soon.
If you want to release a game on Xbox One your choices right now are a) DirectX/C++ b) Unity (available at some unannounced time in 2014).
In addition you need to be accepted into the ID@xbox program and be chosen as one of the special few to get a dev kit, otherwise you have to wait till they enable retail boxes as dev kits - also an unannounced date. Meanwhile practise on windows 8 as the APIs are fairly similar.
XNA is still the only way to ship games on XBLIG for the 360.
Its still fully supported on WIndows Phone 7 and 8 - though on 8 you don't get access to any cool phone 8 features.
It runs perfectly well on Windows 8 too though you cannot make an XNA app that will run in the windows app store. Desktop mode only
Steam fully support XNA (guncraft is 100% XNA and we just shipped on steam) - they auto install XNA3 or XNA 4 and there's several places you can get managed wrappers for the steam APIs we use this one http://www.communityexpresssdk.com/ - its been good for us and the team has been very responsive
If you are learning to make games and you don't want to go the designer engine route (like unity) then XNA is one if the best ways to learn the principles.
Saying all of that Microsoft have not touched XNA for several years now and there's no plans that anyone knows of to start it back up.
So no news on Xbox One support (though Mono.Game will support it if possible), you really can't ship in windows 8 store and who knows about future phone releases. I'd say XNAs time as a platform to ship games is coming to an end. If you can ship on steam I'm sure they will support it for a while yet but I wouldn't be starting any long term (1+ year) projects unless you make sure that your code also compiles in Mono.Game
[Speculation] Microsoft Kodu will probably have some kind of non-programmer-friendly iteration on the new Xbox. For us programmer-types, we'll probably have a new from-the-ground-up XNA-type API. I bet Windows 8 apps and Windows Phone 8 apps will also have some kind of semi-easy migration path for porting to the XBox One. [/Speculation]