What motives would there be? They already offered the crown to one of the Swedish princes, but the King refused it. The Danish Prince came from a line that had rules Norway for centuries, had a wife who was the daughter of the the British King, plus already had a son so there wasn't any issue about deciding between republicanism, finding a new monarch, or the crown bouncing back and somehow making some sort of personal union with Denmark. Plus he was humble enough and required a referendum for him to come over. Having someone from Germany or the Balkans (mostly Germans) would... Well, it would not exactly increase good relations with the British and Danes. The Danes (and the Russians who had a lot of connections to Holstein, and from this came the 'Heir of Norway' in the long list of the Czar's titles.) would see this as the Germans encroaching yet further on the Baltic (Yah, I know Norway isn't really bordering it) while the French would point the past issue of a Hohenzollern for Spain as the Germans trying to get monarchs everywhere. I don't see either the Storting or people of Norway gang along with a German as... well for starters, Bokmal (one of the two versions of Norwegian) is similar to Danish, and Germans may be used to a different style of government than what the Norwegians would want.
I see either Norway option for a republic from the get go (they went with a king partially so it seemed less revolutionary, but here I see the French, Swedes, Danes, British, and Russians supporting it as better than the alternative), establishing a republic later on by themselves (one party in the Storting had republicanism as part of their platform, but when the King calmly asked them to form a government when they had the most seats, they removed it as he had shown himself keeping to the desired role of reigning without interfering with the democratic process), or... Hmmm, suppose it would be fun/horrible to see Norway dragged into WWI.