Actually, now that you speak of C++, in my opinion C++ developers is what the project needs the most. There are currently only a few developers that actively work on the engine (to name them: Günther and Clonk-Karl, sometimes also Mortimer and Isilkor) and C++ together with the huge engine is just something which requires more programming knowledge and experience than creating game content with C4Script. You mention that you know the directX SDK... there is one thing... (look at the date). It's one of the things that never got done because of the lack of Windows engine developers (who know the DX SDK). I can think of many more issues and tasks that must be done or will have to be done in the engine sooner or later. However, I can imagine that you don't feel like working through some list of tasks with no direct connection to some roadmap. If you want do look around in the engine, cling to the people mentioned above.

Also, of course, if you are more interested in level design of settlement scenarios (and other game content related stuff), you are also welcome to do this. Good game/level design is an important skill by itself. The people who currently work actively on game content are Maikel, Mimmo, Ringwaul and sometimes Zapper and Randrian. If you don't want to program something that is done already by one of them, you should talk with them. Also, perhaps they have ideas what could or should be done in the content development. As you point out yourself, there are not many objects for settlement, yet. So the design of settlement scenarios is probably too early - there is no settlement yet. A roadmap of some sort for settlement does not exist neither because, well, I guess because nobody who would then lead the development of the settlement created it yet.

So, basically, if you read about a cool idea here in the forum or have an idea yourself, you can directly start implementing and testing it as a prototype. This then first just goes into /planet/Tests.c4f/ in the repository (folder for tests, prototypes, odd objects,...) but since it is not really defined yet what will be part of the next release, the chances are high that your stuff is part of it if it turns out to be fun.