This affects the End dimension only.

What I expected to happen was...:
All Endermen were to spawn on an Enderman friendly platform to the mob capacity limit.

What actually happened was...:
Instead, no Endermen spawned. Endermen do spawn without a problem on the End island however outside of that boundary if a platform of sort has been built no entities exist. No matter the difficulty, the range from the End island, or the height of platforms, Endermen refuse to spawn.

Steps to Reproduce:
1. Go to End.
2. Leave the End Island.
3. Build a platform out of a any block other than obsidian and end stone.
4. Build a separate platform out of endstone and obsidian.
5. Review spawns.

To my knowledge and tests Endermen spawn only on obsidian and enderstone in the End dimension. This means that any other type of block is treated as an unspawnable platform.

As of this snapshot all Enderfarms are broken.

Even if this was intentional, endermen do not spawn on blocks that have pressure plates.

The enderfarm I built on survival and on a snapshot server was working prior to 14w06b and 14w07a.

My difficulty of course was not in peaceful. You may verify this by checking the F3 debug overlay.