UCMaterial hasn't been touched since 1.14.4 by the look of it, meaning it doesn't support any items that have been added since then. Plus, UCMaterial is quite messy in some areas, and switching to XMaterial means one less (large) thing we have to maintain.
Alternatives
Ignore UCMaterial, resulting in no new items available for use in the GUI or treasure chest structures.
Continue maintaining UCMaterial, which seems like a large project.
Re-reading the UCMaterial class, it appears to actually be derived from XMaterial a few years ago. It'd be nice to be able to shade it using Gradle so it can stay up-to-date.
XMaterial
Why?
UCMaterial hasn't been touched since 1.14.4 by the look of it, meaning it doesn't support any items that have been added since then. Plus, UCMaterial is quite messy in some areas, and switching to XMaterial means one less (large) thing we have to maintain.
Alternatives