Reading Schewe's earlier post *appears* to me to be comparing K3 with K3+Vivid Magenta, not K3+Vivid Magent 4880/7880/9880 with K3+Vivid Magenta 11880, but I agree it could be read either way.
If you look at part numbers, there are new K3 inkset part numbers. So the new Cyan, for example, works in the 9880 and 9800 but the old Cyan only works in the 9800.
Suggests to me there was more to Vivid Light Magenta than the change in the magentas, but not that the 11880 uses a different subset again.
Having said that, if you look at the new head technology it could certainly be that changes were made to the pigment encapsulation to work/take advantage of the new design.
Of course, I feel a bit dumb speculating on the meaning of something posted by someone here...I'm sure Schewe will correct my assumption subject to any restrictions on his commenting imposed by Epson :-)
If you read the thread I mentioned a few posts up, Jeff provided the following information
"Reformulated resin to reduce gloss differential (even more than the K3 inks) and a further increase of pigment density (beyond the K3 inkset). The reformulated resin and new head design also decreases the likelihood of clogging (that head change may also be in the smaller printers–I can't remember).
Epson didn't want to over-promote the reformulated K3 with Vivid Magenta inkset for the 11880 just yet..."
If you read that thread in context, that answer was a direct response to a question about the 11880 inkset being different than the 48/78/9880 ink set.