My cabinet company will make a sample door in the exact style, color. species ect. of whatever my customer has chosen (there are literally 100k + combinations to choose from). The customer receives the door and will sign off on everything. Then I encourage them to keep the door until they are done with the project. Customers love it! They carry their own custom full-size door around with them to shop for accessories. And they can use it to show friends. When we place the order the sample door is credited back, so as long as they place the order, they don't pay for the door. At the end of the project we take the sample back and place it in our sample inventory.
A similar process would be attractive to custom builders. Can you imagine how excited a customer would be if you hand them a model of their future house? I can just see a couple proudly placing their future home on the center of the kitchen table and having conversation after conversation with friends about it. Each of those conversations will be helping to create more customers for you. I do really think there is a future for this idea.
Now, spending 20hours making the file would not be doable for most budgets or schedules, but if we could get the process down to an hour or two it would absolutaly be worth it.