Hi! Thanks for the questions...
I'm not sure yet which features we'll carry over. Not all of them. A World of Keflings on Xbox has a ton of tiny unique features that depend on Xbox Live services, like banner towers, sharing collectible progress through message payloads, unlocking of content based on what other Xbox games you own, Xbox Live Avatar support, unlocking new avatar content from within the game, and a dozen other weird little things. We went a bit crazy on that stuff.
For Steam, much of that will go away.
We don't have any plans for Windows Store releases any time soon, unfortunately.