Maybe I'm missing something, but the exposed surface of the veneer will look the same whether the veneer is 1/42" or 1/8" thick. I'm not sure what you are trying to achieve by going to thicker veneer.
I agree with John V that solid 4/4 crotch slabs will be problematic to say the least.
One "plus" for using "normal" thickness veneer is that when you book match across the face, the veneer will be much more consistent in appearance. When you book match 4/4 lumber, the each set of two leaves is very alike on their inside surfaces, but as you travel through the log, each successive set will be one inch (4/4) away from the set on either side of it. So instead of having a small variation from one book matched pair to the next, you will have the potential for fairly large variations. The thicker the slab (veneer or lumber) the more variation from one set of two to the next.
Personally, I wouldn't even offer to do it in lumber, it will be extremely costly, very risky and in my opinion, probably less aesthetically pleasing. That's where I'd step up and tell the architect, "this is what I what I can do ..." and then explain why, in detail. If the architect says "no", so be it, sometimes the best response is "Okay, good luck, thanks!"
Member