Where did you hear it has been discontinued? There's no official announcement that I know of ;-)
XBLIG is continuing as normal - XNA works and will continue to work on the 360. Nobody has any idea about Xbox.Next
XNA games on Windows Phone 7 are equally one of the only supported platforms - so you have no choice if that's what you want. XNA apps on WP7 will continue to work on WP8.
Windows Phone 8 SDK is not public so nobody knows for sure the state of XNA
Windows 8 runs XNA apps just fine and will continue to do so. They do not run in Metro mode so they won't run on RT based tablets and they cannot be sold in the store as WIndows 8 apps (though you can have a store entry that will link to your own web site to sell it)
Dream Build Play - we never have any idea about that until its announced each year.
XNA is not really a game engine though - its just a managed API that wraps game like APIs such as DIrectX and XAUdio. It has a few game constructs in it to help you get going. SO its was never designed to compete with Unity/Unreal etc
Bottom line however is that there's no XNA team any more that we can tell. So XNA is now what it will be going forward. No bug fixes, no new features (unless Microsoft has some secret project going).
SO whats your future?
If you want to release games on Xbox - you have no choice stick with XNA
If you want to release games on WIndows Phone - right now you can still release XNA games and they will work on Phone 8. This may change in the next few weeks.
If you want to release games for PC and distribute yourself/through steam/etc - then keep going. XNA is a solid API that works well.
If you want to release games for PC and you want to sell them in the App Store or you need DX11 features then you need to change tactics:
- Mono.Game has just released their latest version - a cross platform version of an XNA style API that requires little to no changes to your code. The project is very active right now.
- Sunburn has announced their post XNA plans http://www.synapsegaming.com/blogs/johnk/archive/2012/10/23/announcing-sunburn-2-1-platform-independent-game-engine.aspx - worth a look if yo do want a graphics engine that handles shadows shading etc.
- Or switch to Unity
- Or switch to C++/DX11
If you just want to learn game programming then carry on as you are with XNA its an excellent way to learn the skills without worrying about memory issues, C++ syntax or strange DX11 rules :-)