With the new 1.20 update, a new feature known as armor trims will be added, which allows for armor to customized.

I was wondering if you could see when 1.20 come out, whether these armor trims could be used to add custom armor, without the need for Optifine.

(I understand you cannot know for sure until 1.20 comes out. I am just preemptively asking)

I haven't looked into the 1.20 update yet, so I don't know whether I can use it. Since this plug-in supports many minecraft versions and this feature would only work in 1.20, I don't expect to work on it anytime soon.

The FancyPants custom armor system turns out to work on 1.17 and later, and is much more powerful. Therefor, I won't implement custom armor trims.