Just as a remark: it's no advantage that the DQ's superstructure is made from wood, but it's also not a disadvantage from the perspective of protecting people from the consequences of a fire. Please, let's be very careful with statements like this. You know how journalists and politicians are: 1,000 people say "A", 1 man says "B" --> journalists and poilticians say: "See, B must be true." just because it's the easiest answer to their problems.
I think it's very important to think differently about a fire on board of a boat/ship, and in general with buildings:
First of course there should be no fire at all, so all material that doesn't catch fire easily is a big help. But look at cruise ships: There is a lot of plastic chairs, etc. - this stuff catches fire much faster than any material used for building superstructures. Put a cigarett on a wooden chair and a plastic chair: The wooden chair will not catch fire, the plastic chair starts melting and might start a fire. SO it doesn't make sense to discuss this at all as the fire hazard is the same on any kind of ship, boat and building.
But then it's very important how long a structure withstands the fire until it collapses. That's much more important than the question whether the material itself is burning or not, because the dangerous fumes (which are the main problem in a fire, not the flames and heat itself!) are being produced by burning furniture etc already longh before any kind of superstructure catches fire. Wood burns and is being consumed by a fire (in case of the DQ, slowly because it's hardwood, not Pine or something similar!). Metal doesn't burn, but it's melting! And it transfers heat quickly throughout the structure as it's a very good heat conductor. While wood is isolating the heat and keeps it local.
Passengers need to be evacuated before a structure collapses. Ask experiences firemen - they tell you that they feel much saver entering a burning wooden building than a metal construction. That's because wooden structures are very stabil even when burning and it's easier to estimate when they collapse, while metal when melting are collapsing all the sudden (see WTC and other steel buildings).
By the way, the DQ's superstructure is not completely made of wood. Many years ago they built in metal structures within wooden colums to give the structure even more stability and then they wrapped the wood back around the metal (sorry for my bad English explaining this, but I think you get the idea). Yo udon't see the steel, but it's there.
To my understanding that's the best structure a river boat can have: Solid steel stabilizing the structure is protected from melting by slowly burning hardwood covering. And let's not forget the fireretardant paint on the wood all over the DQ: This paint even prevents the wood from burning at all for some time. And wood doesn't melt! So as long as the paint is protecting the wood, the structure is neither burning nor melting.
Let's get people understand that wood has nothing to do with campfires. You won't make a campfire with steel, you do it with wood. So the perception is that wood is a fire hazard. NONSENSE, I say! Let's not get the politicians away with such cheap excuses. We're living in the 21th century. Let's make the politicians use their brains instead of making decisions based on kindergarden-level perception and knowledge of technology.