But, anything can be done with the right effort.
For the Z3100, the following possibly could be done:
-- A new red ink formulation that is labeled something other than #70. This cartridge, of course could be made to fit the Z3100.
-- The existing printhead design continues to be used.
-- A completely new driver and completely new firmware are issued to handle the new ink. Similarly, the HP Printer Utility is updated.
On the user end, this would require flushing the red line or printing enough solid red pages with the new cartridge in place to use any residual "old" red. It might also require replacing the Red/MK print head. And, of course, installing the new driver, firmware, and utility.
Can this be done? Certainly. It's not physically impossible. The real question is does HP want to, and what is HP's business case for doing so (or not doing so). Though I was under NDA for the Z3200 and was told the Z3100 under no circumstances could be field upgraded, anything is possible. I have absolutely no special insight on this topic, just my decades of experience dealing with printer manufacturers. This is nothing more than pure conjecture on my part. All that said, I'm only occasionally disappointed in the red performance of my two Z3100 printers.
But, I do wish for something on a completely different topic: I hope that the successor to the B9180 is fully compatible with the HP Printer Utility software.