ICx / ICE 4 are meant to replace the IC/EC trains first (which are slower than ICx) and later ICE 1 and 2. It seems that their slightly lower top speed shouldn't matter because of improved ac-/deceleration and relatively frequent stops (every ~70km). ICE 3 would do the 300km/h bits with longer distances. That seems like a good idea to me.
I'd like to ask on a source for your claim that ICE 3 "are scheduled to be reduced even further." The series 407 trains are just being rolled out.
Also, by definition most tracks will always be slow because there are many local / less-used tracks where such speeds simply don't make sense. Most long-distance tracks are pretty fast, and lots of upgrades are being built or in planning. I find your point misleading.
Meanwhile, the more ubiquitous current 280 km/h models are scheduled to be replaced with a more economical 250 km/h one – and they won't even reach 200 km/h on most tracks.