I think you saw a lot in terms of guitar body design. But designers don't cease to amaze. On Internet, I noticed an interesting guitar - Villanizer.
Yes, steampunk style is very attractive because it allows creating very illogical designs. And sometimes you can even stick a few gears and proudly hang a label "steampunk." Nevertheless, an interesting approach is evident here. Protrusions, imitating rivets, create impression of an iron construction. Image of rust and abrasions is always a good solution. Bronze hardware are also an interesting solution. Also in the gap, you can see something that gives feeling of an iron frame. Another interesting solution is placement of a pressure meter on one of edges. Designer thought out the concept of steam machine well.
On video you can see how it looks in work.