I think it's a great idea and would only enhance your reputation as one of the premier builders of finely detailed model railroad stock but, if you're going to take the plunge, I would consider opening the market up to an even larger pool of potential buyers in the O36/O42 layout range and make them in either 15" or 16" size.
Unfortunately, 18" is still too large for those of us who would love to be able to run scale equipment but simply don't have the available space for a large layout and who would still like to own show-quality pieces.