Because Epson has the switching of black inks, I will not purchase another Epson product until this is rectified. Heck, i never 'upgraded' to the 4800 from my 4000 specifically for this reason.
Regarding the 8 versus 12 ink debate, I will let others chime in to represent the 12 color machines on the market. It is my experience that black and white output on the Epson is very close to that of the Z3100 series printers, so I don't consider that a major difference. From a color standpoint, from everything I have seen with my own eyes is that the HP excels in areas that Epson does not, and vice versa. Perhaps Epson's science behind their inks and mixing is more sophisticated, thus requiring fewer inks. I just don't know. It doesn't appear to be much different from an actual output standpoint, though. If Epson doesn't need to have more inks, why should they move to 12 inks? Marketing? Perhaps. There is always room for improvement, but I think Epson would be better served solving the switching of black inks first. This would make a huge difference to many of us.