From a production stand point, the major manufacturers have addressed about as much variability as their bottom lines will allow. Heck, it's only been fairly recently that the south-paws have been able to buy equipment made for them. As a quick side note, Savage has recently introduced something along the lines of a semi-customizable stock, with a variety of recoil pads, spacers and cheek pieces.
Building molds, I know that the customer is going to squeeze every nickel out of them (including running them past their maintenance schedule -- as long as it's making good parts it's making money). Why? Making an injection mold is an arduous process that often reveals several needed revisions along the way, and when said mold runs upwards of $1M you can bet that it's going to take time for the ~$10 in plastic/shot to pay off the mold. The company is going to have already determined that the sales will be there to support the project.
Yes, there is a market for longer LOP stocks, the aftermarket. Places like Boyd's fill that market, because it's easier to shift a work offset on a CNC one-off than to build, set-up, run, maintain, tear down, and store numerous, sporadically used molds. Or, as another poster said, just buy a much much cheaper (by comparison) spacer.