It would be great to have more HSTs, but before that it would be really nice to have the LZB (and similar systems), so that we could run, for instance, the DB BR 182 at 200 kph between Leipzig Messe and Bitterfeld (please, bring back the old speed limit -which is the real one, BTW- of 200 kph).
We'd need new carriages as well, the DoSto are only certified for 160 kph. And the trains going 200 km/h don't go through the tunnel in Leipzig. We'd need the surface part of Leipzig Hbf for that.