I am by no means a programmer but I think it's the 2 dye channels are tied to say, "Material A" and "Material B", and A/B aren't exactly "uniform" across all pieces of gear. So B may be tied to trimming on one piece, and on another it's tied to... hardly noticeable details like buttons. Then there are pieces that will have gradients (the level 100 GNB goat) that are separate materials and are also undyeable so you're stuck with them no matter what. It kinda feels like the issues the new dye channel set out to solve are still there in many regards, so... 3 dye channels when?

Unfortunately I feel like dye channels are unlikely to be changed because they might have the reason of "well some people might already like how the dye looks so we don't want to upset them".