As of MC 1.11 pre-1, elytra texture transparency is completely broken. Pixels with alpha transparency appear opaque now. Relates to MC-98327, but doesn't happen with specific items, instead this is a constant problem now. Transparent elytra textues worked fine in 1.10 and are used in many resource packs. See screenshots for 1.10.2 and 1.11-pre1 comparison. A transparent texture for testing is already attached to MC-98327.

NOTE:
This bug may be a result of fixing MC-109587. Transparent elytra textures worked fine in 16w44a and previous snapshots, even after other elytra-related bugs like MC-99353 have been fixed.