As far as I know there is no official information on this, but there have been some rumors.
Microsoft is said to plan a version of Silverlight 5 running on the Xbox 360 and with this they may open up the platform some more. Look at this article for instance: http://www.tomsguide.com/us/Free-To-Play-Apps-Xbox-360-microtransaction-silverlight-5,news-10800.html
But this is still only a rumor, Microsoft has not even announced Silverlight for Xbox in public yet.
That there will be a version of Silverlight for the Xbox is quite obvious though, look at the documentation for the INotifyPropertyChanged interface for instance. Here the supported platforms lists the Xbox 360 :-)
This does not fully answer your questions, but I think it is the best answer there is. Microsoft will probably announce a new platform (Silverlight) for developing apps on the Xbox 360 quite soon. This new platform will probably allow for more ways to publish apps, but that has not been confirmed.