The subtext seems to be 'you're lucky I even made these' and 'just stack some washers dummy' which is real nice considering I dropped $50 on your joystick. Yes, I was aware I could stack washers, it's not like I didn't know how to make it work.
Your delivery of the subtext is much harsher than I would ever consider making, but unfortunately there are some basic realities at play. The first is that there are two options for specialized items like this. The first is to do everything one can to keep the costs of production as low as possible, and within reach of as many as possible, while attempting to cover as many of the typical users requirements as possible. The other, is to cover every possible user requirement and take a "the sky is the limit" approach for pricing. While the latter might seem attractive at it's onset, sticker shock would likely keep those who would be more than happy to have the former within the limits of their budget, from considering them.
Could I include a plate to make below panel dustwashers (which is no longer the preferred placement by the majority of builders) a part of the restrictor add-on? Absolutely. But due to the extra material and machine time to make them, it would double their cost, and the vast majority would be paying extra for a part they tossed in the bin. I could also simply add these plates as an extra option, but I'm willing to bet that most would simply use the solution you did, rather than paying the extra for the part. So that limits the market for such an item to a small percentage of a small percentage, of an already very small market.
But in the end, yes, I could have simply left the Dominux8 as an 8-way only, with the below the panel dust washer capability exactly like that of the WICO, and sheltered myself from some of the colorful terminology used in this thread. Is that really the approach members of this community would be more likely to appreciate?