Is it a wild guess if I write that you started with the three 4000's that have MK and PK aboard ?
Individuals, small shop owners, starters and shops that will never own 8 printers will like the universal ink set of one or two printers for gloss + matt in both B&W and color mode. With two if one fails you still have the same flexibility. The shop has to diversify its equipment anyway for sheet or roll processing.
The five 17" you have can easily be replaced by two Canon iPF5000's. One or two Z3100's or iPF8000-9000 will do the roll jobs.
Actually we started with the 7600, and it has never had PK ink in it.
You are right, there are some that both matte and photo black are a very important feature. I have never disputed that point, and if that is a must have for anyone, then HP is probably the best option right now.
However, there are many of us that have no use for that feature at all. I do not need it for my business, nor do I need the expense of a built in color profiling solution. From a personal perspective, I wouldn't mind a good printer that has both, even though I rarely need matte, so it really isn't a major consideration for me. As I mentioned I am much more interested in the performance of the new inks, and also just curious if there is any "official" word (in other words, someone that has actually seen a demonstration) of no mk/pk support.
As far as replacing the printers, not sure why I would do that. The 4000's still have their original PK ink cartridge installed, despite printing thousands of prints. We have never done a single ink swap in any of the other printers. Each printer is dedicated to a particular paper size/type. The sheet feed mechanism of the canon seems to be awkward (we have one) and not quite as reliable (more jams). All printers are also dedicated to a single paper size/type. Since labor is the biggest production cost, and we ship all product the day after recieving the file, multiple machines is far more cost effective and efficient. Were I to replace all of them, even with the added speed of the canon and HP, I wouldn't have fewer printers, I would just need to run them a couple of hours less per day. Since these printers run 12-14 hours a day during peak times, I would be surprised if the heads in the other printers would hold up under that much production. Am I unique? Perhaps in the fact that landscape photography is a serious hobby so I frequent sites like this, but I think there is a large part of Epson's installed base of these printers that are production facilities that operate similarly.
I hope Epson does eventually solve the mk/pk issue, so we can focus more about the quality of the output. I have an ipf5000 and had a z3100 for about a month. As far as quality of output is concerned I see nothing the indicates that either of them can produce a better print ... all of them are capable of producing outstanding results. That would be the most compelling reason to switch.