Do a manual nozzle check on an 11880 and you get 9 colour swatches (it runs Vivid Light Magent, Light Light Black, Photo Black, Light Black, Light Cyan, Cyan, Vivid Magenta, Matte Black, Yellow).
So there's no gate or swap. There's 9 channels in the print head for 9 inks. In the single print for the nozzle check it puts down both matte and photo blacks. You can see the difference between the PK and MK. The MK "falls between" PK and LK on Epson Premium Luster 260, but not halfway - to my eye, it's about 25/75 split and closer to PK, but that's not a scientific test :-)
For more confirmation, go into the maintenance menu on the control panel and into the cleaning menu. You can clean channels in groups (rather than all at once).
The available combinations are C/VM, PK, MK/Y, LLK/LK, VLM/LC. So all pairs except for PK (well, there's 9, so you can't have all pairs!). If the PK and MK were simply gated then the option to do PK by itself couldn't exist.
So there's no doubt it's a 9 channel head - one for each ink - and there's no "swapping" so there's no loss of ink at all and no delay at all.