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.
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There are a lot of blocks (all of them ?) who doesn't allow semi-transparent textures. I tried to make a glass with the flower pot, but you can't make it translucid.
@unknown that's intended to prevent X ray packs.

Why is this suddenly "works as intended"? The whole point of fixing MC-98327 was to make transparent elytra work consistently so resource packs can use them. It worked fine after all the other elytra fixes too, so why wouldn't it now?
Added possible origin of the bug (fix of MC-109587) to description.