"If they build it, they will come."
That being said, there is no off the shelf, bolt on, intake manifold, period. The closest we have is the Xcessive plenum which takes some modification to make it work to its full potential. It is also not an off the shelf bolt on plenum, but it can be customized to what you want which is nice. I have one of the Xcessive intake plenums and there was a bit of modification required to make it proper. This does not bother me as i am very hands on and take enjoyment from working with my hands. A lot of people do not have the tools, knowledge, or motivation to do this. It is also just the plenum and not a full manifold, so again there is more modification to the stock lower runners to make it perform its best.
It is my opinion that if someone came out with a bolt on manifold that was around the $800-1000 mark it would sell. A few will sell right away as some people do want them. But what needs to happen is back to back testing on a dyno to show the gains. Going back to your point, most people on this forum are not willing to take a risk and test it for themselves, not a great attitude to have for a community that wants good products.
I am going to test the Xcessive plenum I have with the stock TB before the car is put away for winter, then I will do another test in the spring when I upgrade to the Q45 TB and 3.5" intake piping. I also want to change my Mazworx header that has not gotten the best reviews. I am willing to share this info but it is happening on my time, I am in no rush.
All in all, if someone made a full cast manifold that is proven it would sell, it would be a risk for the producer but over time I am sure they would end up making a profit.