German starters in the middle of the net are getting older certainly - Ssuchke-Voigt is almost 31 years old, while Fürst is 29. Stefanie Karg who can join will be 28 in October. Both Berit Kauffeldt and injured Anja Brandt are 24 in this year, so they can be starters for next few years when Ssuchke and Fürst will retire, if Karg isn't in NT (or she also retires). And idea with Schaus as MB in NT is probably given up being unsuccessful, moreover she's also not young (30 in November).
From youngers mentioned were Leonie Schwertmann (20), Alessandra Jovy-Heusser (23 in September) and Rebecca Schäperklaus (tried also as OPP, 22 in July), however last two can be not so helpful for NT. What about Celin Stöhr, also not recommended as Jovy-Heusser and Schäperklaus or maybe a bit more skilled? There is also Melanie Keil, but she studies in the USA and I don't see her as a good choice for NT at all
How about Silge's performance in DVL, Matthia? You see her as a great prospect
About Schaus: she has played all attacking positions and MB definitely was the best in her career, so I wouldn't say it was unsuccessful. The reason why she's out is that Guidetti wanted to work more with younger players for the 2013-16 period, so some of the not so good old ones (Schaus, Matthes, Burchardt) were cut.
Schäperklaus has been playing pretty well in her club recently but I don't see her making a career on international level. Stöhr is Anja Brandt 2.0, decent blocker but terrible attacker. Jovy-Heusser is like that as well.
Silge is usually not starter in Münster but gets enough playing time. Sometimes she plays as MB-style OPP but also with backrow attacks, but usually she plays as MB. Recently she's starter because Schwertmann has a back injury and she plays very well. In the match against Schwerin Felix Koslowski gave her the MVP award and in the first pre-playoff match she got 7 blocks. The last German MB who played so well with 17 was Fürst, Silge is much better than for example Kauffeldt was at the same age, so I have high hopes for her