to last decades, to be easily repaired and updated
Does anyone actually think anyone will be using the same class d amp in 20-30 years? With the way the technology is still evolving, I find that bordering on pure fantasy. I see no reason why having something that is easily repaired (what can be easier than swapping out a module?) or updated should add significantly to the price.
Linear power supplies are have for the most part been superseded by smps. With all the class d amps on the market using smps successfully for a decade or two now, there is enough data to show they are in general reliable and that their performance is more than satisfactory. But then, nothing says quality like a big, heavy transformer and flashy expensive case, especially to those who are willing to pay a premium for racing stripes and metallic paint. Vrooom!