Point 3 is only really software, and point 4 requires components that cost $ not $$$ (and software) so I definitely agree with you there. I'd love to see the ability to load samples into the piano section (or even some "pianos" that are actually string, horn, pad samples). Regarding points 3 and 4, the particular memory that Nord uses (NOR flash, I think?) allows it to stream directly but costs much more than the NAND flash in your SSD, for example. I think this has been discussed here in the past, in that an extra $100 component cost can easily translate into $500 addition to the purchase price.
And also, yeah, market forces. If Nord can sell sufficient quantity of a board for $5000 at 40% margin, there's no incentive to sell for $4000 at 20% margin.
Cheers, Mike.