Let’s talk real wood, shall we? 
Here are two rather extreme samples/examples, but it’s getting less and less extreme by the day, since orders keep getting weirder/crazier/whatever.
First, let’s have a look at some basic body shape for an E-guitar.
See how intricate the fiber structure is?
Now beyond that (and beyond tastes) are actual orders, like this one:
Now that’s wood grain orientation. I had to ask my friends at Halo Custom Guitars for the preview. Most of my time spent doing custom shop work ends up like this or much, much more complex (17-ply necks with 5 or more different wood essences, headless with each-string-a-different-finish-tuner near the bridge, up to 14 strings… you name it, we do it)!
There’s not only wood grain and fiber direction, as you can see: burl tops and Black/White dreamy ebony fretboards are now commonplace.
If I can’t give the player a proper preview of their dream instrument, then I can just leave with the specs sheet. I can’t possibly do that and I can’t imagine anyone in the biz of “hyper-customizable” do that as well. Only one or two in 300 orders are not cancelled, even with a preview.
I’m sparing you swirl finishes. Sure, it’s an extremely niche market and few players can afford custom products.
I thought it was time to show you what I wanted to but couldn’t due to rendering limitations.
I’m also working on furniture. No matter if it’s luthier or furniture maker, same issues IRL and same issues with rendering.
The real issue with wood is that it’s too complex to get a “quick fix”.
I can understand: taking realism to the next level is a really heavy thing used by very few people… and it’s too heavy for iPad apps, perhaps (though Shapr3D works on 3 platforms).
And I can understand why some people did it… but it’s done on huge desktop rendering powerhouses costing twelve legs!