Currently elytra are incompatible with both capes and chest armor. This causes any animation depending on vanilla cape animations to cease working when wearing an elytra. Similarly, when not wearing elytra, any animation or model derived from it does the same.

There could be an option to force the elytra model to always be equipped but hidden by default. This model may need to be modified for compatibility with both capes and chestplates. It could then be reenabled with the "wearing elytra" animation layer if needed.