Ich don't know how Prussia treat the Slavic Czech Catholic population. They had a harsh expell- and Germanisation policy against the Poles.
The Czechs probably get much the same. Prussia didn't encourage local differences.
Could be quite a problem if they take all Bohemia. If OTOH they just take the "Sudetenland", You probably see the Czech minority drifting across the new border back into Austria. Fifty years on the ceded territory is probably overwhelmingly German - sufficiently so that Germany has a good chance of keeping it even at Versailles, if that isn't butterflied.