that's very interesting. I keep having this internal back and forward between just a big printer or adding a small one. There are good arguments for both. One lets me focus, save cash in upfront costs, and time in learning and setting up. Two provides enticing flexibility in being able to run out very small prints straight off cut sheets with no trimming afterwards. Am I right in assuming that small prints can be layed out onto a roll and then trimmed after, but this requires decurl and trimming, as you say. Plus with what you have just said the refilling cartridges taking the cheaper ink from bigger carts, which sounds great!
I suppose it's not a big deal anyway, even without the ink price advantage, if the overall convenience of the desktop printer for small prints overrides the costlier inks in small carts I could simply factor this into my print prices by increasing them, but its still worth considering. It's an economic game when in it for actual business reasons and every factor contributes. On this topic I wonder too if that limiting the minimum print size to sell to something not too small (around A4) results in better revenue because do some buyers tend to go for the smallest print size on offer. Even if some more research results in my smallest print being A4, then you mention about promotional items and the small format would be valuable here.
I was actually looking into the Canon Pro-100 (a dye printer) and it's use with the swellable papers which hold and protect the dye and enable it to be quite resistant to fading although not to the level of pigment. My thoughts had been to possibly use this for the small version printer and run off snappy and vibrant prints because the vector artwork I have is colorful in nature, solid areas of bright color and sharp edges. In practice however I'm still evaluating though because I think pigments have more subtlely which may make the edges of colored areas more definite and tangible. The only way I can tell if dye vibrancy would trump pigment nuancy would only be if I get into actual testing it and getting samples of my specific work. But dyes somehow appeal, and I will be staying with the pigment printer for my large format, most likely the Canon 8400 is favourite at the moment.
From looking around (I searched 'Pro-100' in this forum for example) it seems that the dye printers aren't a favourite of printmakers and pigments are king. My search turned up only a handful of pages on the Canon dye printer. Also I thought dyes were cheaper inks than pigments? I would want my buyers to display their prints and unless they tip water onto the dye print hopefully it would still be suitable.