An exact wording would be appreciated. So, technically, there can be a "wood nature"? If that's the case, let's take a look at the "three natures" argument I used before, the one you explained as
"Fire Release + Wind Release in tandem = pseudo-Kekkei Genkai Scorch Release
Steel Release + Lava Release in tandem = pseudo-Kekkei Tota ??? Release".
If we consider a combined nature as a nature of its own, in this case steel and lava, the pseudo KT doesn't fit the definition of KT as we know, it would be just two natures, while KT are three. With the Scorch Release example, it works because they are two natures being used together, but not really blending. If we consider each combined nature as each of its components, Steel Release would have to share a component with Lava Release, otherwise we'd have a four nature combination, as I explained in my first post using this argument.