I really wouldn't like to see Oberösterreich disappearing, most of this area the Traungau was controlled by the Von Chiemgau margraves of Styria (later dukes) in fact Styria is named after Steyr in the Traungau now Oberösterreich where their dynastic castle was located (originally Styria was a march of Carinthia); removing it would IMHO not make the map nicer at all. IMHO the current border between Austria, Bohemia & Moravia and Bavaria is very nice; OTOH I wouldn't mind a version with an extra Znojmo being re-added to Bohemia/Moravia). Especially since the map isn't only for 1066, but for the entire period from 1066 to 1337.
I'm still thinking of adding a Cilli/Celje province by splitting it from Steiermark, redrawing Steiermark, Carniola/Krain and Carinthia/Kärnten a bit in the process and potentially enabling a duchy of Styria; however that perhaps shouldn't be in a standard mod version.
I agree with your point of the rivers, I've noticed that too
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