This is just a little refresher regarding longevity. It's a table from my Eboni-6 PDF that is based on Aardenberg-Imaging data:
Delta-e at 60 Mlux-hrs Light Exposure
Average 50% test patch
Eboni 3-MK, PA 205, Print Shield spray 0.2 0.2
Eboni 3-MK, H. Photo Rag (HPR) 0.3 0.2
Cone Carbon Sepia, Museum K, HPR 0.4 0.2
Epson ABW, HPR 1.0 1.6
HP Vivera, HPR, neutral only 1.1 1.4
Cone Neutral K6, HPR 2.2 2.9
This plus the huge cost differences will guarantee that there will always be an enthusiast market that starts with carbon and ads only the best color toners, if needed.
Paul