We are planning a Christmas Market trip this December, but would also love to visit Zermatt. Any suggestions on a scenic route through small towns, including Nuremberg, to fly out of Munich?
No recommendations re: your question, but if you stay in Nuremburg, which is one of out favorite towns with an incredible market (we go every other year to do a Market Trip) - we love to stay at Hotel Victoria there. It is super close the the market, includes an amazing breakfast, is next door to the local vendor craft area, and right across the street from the train station - we always take the train to Munich and fly home from there. Munich's Markets are UNDERwhelming, but it's a great place to fly home from. If you need great tour guide in Munich - we love bighattours.com - he does a great tour to Dachau Concentration Camp, a good Third Reich Tour, and City Tour. The train from Nuremburg to Munich is about an hour and super easy.
Zermatt is really quite far from Munich by train, it takes a whole day each way... And in December, the risk of poor weather is very real. Going all the way there to NOT see the Matterhorn would be a shame.
It only makes sense if you intend to visit other places in Switzerland. Do you? If you don't and just want dramatic mountain views, then perhaps consider a day trip to the Zugspitze from Munich. It will be COLD but the views are incredible on a clear day.
Winter means ski season in the Alps, so don't count on it being "off-season" as far as booking hotels, etc.
And beginning Dec 18, it will be super prime time for family ski vacations. Before that date, you could find some bargains.