Good questions. We will have a release each month at
http://DeltaEngine.CodePlex.comNow everyone can take this version and start developing their game or application. They might also consider helping out with some libraries or integrate their own libraries, etc. This is what we want (unlike most projects on CodePlex or many other sites were only the internal team does some work). These changes will be merged back monthly by us, which will probably take up most of our time in the future (cleaning up code, making sure it all works fine on all platforms, etc.)
Even right now we have many different modules for each namespace of the delta engine (multimedia, graphics, input, rendering, etc.) and while you can sometimes use several and mix them, you will stay with the defaults most of the time. And even if you decide you like for example DirectX 11 better, you just have to change the graphics module setting and the rest can stay the same. It is even easier for physics modules or input modules, you don't need to recompile, just change a setting for your project and now you are using some other physics engine.
Having lots of choices is actually what we think is most useful for most developers and what is really different from most other solutions where you have exactly one choice and if it does not fit you, you are mostly out of luck because it can't be changed or is very hard.
To let things stay easy enough for the beginners we will provide the most stable and basic features as the default settings, which means it just works, but it won't be the latest greatest thing (we don't have to expect that every student now can create Crysis2 ^^).
Last but not least: Yes it is true that it takes a lot of time to implement and test all libraries, but most work is not actually supporting something like PhysicsEngine X or Y or adding support for Kinect via some SDK. It is way harder to find a common interface that works on all platforms and devices and provides enough flexibility to do what you want (I always say this is 10 times harder and takes 10 times longer). But once this work is done it is relatively easy to add more and more libraries. We also think adding libraries, adding missing rendering features and especially creating tons of open source games is what the community can do best (way more people out there than our small team).