Taking Mark's post as a sequence of questions:
Yes, you can convert the R2880 to monochrome. Plenty of people have done it. Inkjetmall sell carts and inks and provide a turnkey system. They're not the only suppliers.
Yes, you can get a higher dMax than the P800, if high dMax is your thing. Inkjetmall recently released their new HD Photo Black and Ultra HD Matte Black inks that deliver significantly higher dMax than OEM. They're intended for monochrome printing, although you could use them in a color OEM printer and reprofile. I'll leave readers to check the higher dMax claims themselves.
It's true that some of the pure carbon monochrome systems that provide the most longevity are a long way from neutral, such as those advocated here from time to time by Paul Roark. But if neutrality is your thing then the Piezography Pro inkset delivers a neutral tone and moreover allows fine tuning of neutral for the impact of different papers. Again not the only neutral solution but the quickest one to point to.
The point of my previous question was not to suggest that you try one of these systems, but to check what your comment "
Not worthwhile going to the trouble of dedicating an old 2880 to B&W only" was based on. Speaking purely for myself, there are printing systems discussed on this forum that I'm envious of and others that I'm skeptical of, but I would hesitate to dismiss a system that I hadn't tried myself and hadn't done the research on. The P800 is a great little printer with much to recommend it, but monochrome practitioners often look for more.
This has drifted way OT, and to get it back on-topic I will report that the software that most of these third-party monochrome systems rely on - QuadToneRIP and Print Tool - seems to work under Mojave, with the exception that PSD files are not currently working in Print Tool but TIFF files still are.
The first question is whether it's practical to convert this particular 2010 printer model to monochrome - who's done it and what success have they had with it? I'd want to see evidence before recommending this. The second question before looking at anything else is the DMax you can achieve with a P800, especially in ABW mode - the answer to that one, as far as I'm concerned, is that I've seen none lower from anywhere. Looking visually and statistically at the tonal gradations it produces, they are superb. I think I've seen inkjet B&W prints made in every which way and I believe the P800 stands up well to all of it. So no, I have not tried converting a printer to third-party B&W ink systems. I know many people really love them, and that's fine, but speaking personally I don't see the point. That said, my mind is always open to obviously superior methods, but I'm not feeling compelled to invest in it as an experiment given what we have on the market today. It may be also worth considering a point recently brought to my attention by an industry professional, and sounds plausible - that when you have colour inks available to a B&W printing process, used with good ICC profiles they can help neutralize the effect of non-neutral papers in a way that B&W inks alone cannot do - perhaps useful if you put a high value on apparent neutrality through the tonal range.