We might be heading over to Norway in 2019 - but here is what we gathered so far:
1. The Iceland cruise doesn't quite visit Norway proper - so to speak. It has two outside stops (Alesund and Stavanger), but that's not really the same thing as going into the fjords. So, while it's great that you get to visit Iceland and Norway in one cruise, you might be a bit disappointed by the Norwegian portion if you are after the must-see Norwegian attractions.
2. Ideally, you want a cruise that goes into the fjords. The two UNESCO World Heritage fjords in the southern portion are Geirangerfjord and Naeroyfjord (though there are quite a few actual fjords all along the coast). The ports are Hellesylt/Geiranger and Flam. Another great alternative is Nordfjord, where the ship can go all the way to Olden. A combo of one or two of these fjords is what I would look for in a cruise meant for Norway.
3.
DCL's Norway cruise on Aug 25, 2019, does visit Geirangerfjord and Nordfjord, and we have our eyes on it. We are very much a DCL-focused family, but this particular cruise is a bit late in the season - which is why we haven't pulled the trigger yet. We just might.
4. Other alternatives aren't too bad if you can do non-DCL. Princess has an itinerary that combines Iceland and some of the Norwegian fjords (incl. Geirangerfjord) in one trip. Cunard has one that goes even further up the coast. MSC Yatch Club has an itinerary that visits both Geirangerfjord and Naeroyfjord in a 7-day sailing a few times over the summer.
5. An alternative is to do a road/ferry trip to Geiranger from Alesund, but you need at least 10 hours of docking time to do it safely. The Iceland cruise doesn't stop in Alesund for long enough - though, ironically, the actual Norway cruise does.