Sylvain,
>INKS ...If I understand well what you wrote, there is no real alternative to Eboni if one is willing to stay on "pure carbon" (if we except Piezography, of course). What is your feeling about Eboni 1.1?
There is no carbon ink I know of that is the same as or as neutral as the old, original Eboni MK and it's dilutions. Eboni 1.1 is said to be the same carbon grind, but with a state of the art dispersant. That may be true, but the new dispersant made it more like the other MK inks. It's still slightly more neutral that the others I tested, but there is a reason I added the light blue toner. I concluded it was still the best place to start.
>I tried the glossy carbon ink from MIS, and I found it very warm. I did not find any glossy finart paper able to make it more or less neutral (such as Epson Hot Press bright, for example).
Inkjet carbon (i.e., carbon that is finely ground) is warm by nature, except when it's at the 100% black point. On inkjet paper (coated paper) it's warmer than when on a paper like Arches. Glossy carbon is warmer than matte carbon. And when glossy carbon is on glossy inkjet paper, it's very warm. I, too, have found no way to make a neutral glossy 100% carbon print. The good news is that with the Canon based light blue toner, the print can be more stable than a silver print.
>PRINTERS ... The 3880 is actually a good machine. But I wonder if it will not be obsolete soon?
I'd worry about availability of carts for the replacement printers. Are they out yet? If we can get carts and if QTR supports the printer, then any Epson is probably a viable platform.
> [I]t is a pity that the new "cartridgeless" Epson printers cannot be used for carbon inks...
See https://epson.com/i/C11CE71201. That black ink 774 is a carbon ink that appears to dilute well with the generic base. It's slightly warmer than Eboni 1.1, but if all else fails, we have an Epson carbon source that is very inexpensive. That may be particularly relevant in non-US markets where Eboni MK may not be easily available. With no QTR support (among other things) I'm not sure the printer is appropriate for serious B&W, but I'd guess it and the other ET printers will work with carbon inks. I have used them in my WorkForce 1100 for many years (though I now have Noritsu dyes in it).
Paul