Ok,I don't think anything can be a spoiler since everything in the series has been out for a while. We are all speculating and not divulging anything that isn't readily available.
So, the art looks like it epects blimps rather than dirigibles. That sort of makes sense since aluminum will be expensive to make without electricity if not impossible with current Safehold tech. Steel will require too much lift to allow for enough cargo in any but the largest crafts. Even then the amount of material and maintenance the airship requires in relation to the cargo it carries is simply too high for commercial use. Even VIP transports would struggle to make an operating profit let alone provide an adequate return on investment. This doesn't even get into the static elecyptrical aspects of steel. Solving for that is lightning strikes is possible, but steel still risks sparks from physical contact.
I wonder how big a wooden derigible can be and how much cargo such a frame can support? I suspect not very big at all, but senough for military scout duties. It's possible to construct the frame without metal nails, using wooden pegs, glue and steel thistle straps to provide additional support. That is labor intensive construction, which means expensive to build. Still, such a craft is viable.
Now back to the cover art. Those look like blimps carrying cargo from tethers. The gondola with the props and engine hangs from other straps. If this accurate, the blimp can't retain shape well enough to move really quickly. That argues it is for short hauls only.
