I think you are confusing ink cartridges and waste tanks. The r3000, I don't know about the others, holds all nine cartridges and swaps PK and MK automatically, there is no need to physically swap cartridges. The swap still consumes ink, because the two share a channel, but there is no purging of all colors on a PK/MK switch.
Ok, they did add a 9th ink tank spot. But it still dumps lots of ink when switching between the PK and MK tank. Their specs on their webpage state switching one way dumps 1ml or ink and the other way dumps 3ml or 10% of all ink.
For the r3000, the ink cartridges are 25.9 ml, so nine of them would be 233.1 ml. In economy mode a two way switch uses 1 ml of ink in each direction, or a little less than 1%. In standard mode it uses 1 ml in one direction, 3.2 ml in the other, or a little less than 2%. It is still wasted ink, but not 10%.
The older Epson 17" 4000 had separate PK and MK nozzles, and the current 60 inch 11880 does too. So it isn't like they are unfamiliar with the concept.