This is more of a glitch fix than a suggestion, but wouldn't it be cool if Endermen dropped the blocks they are carrying when killed? This would provide a more realistic feel to killing them. Doing this would also serve as an easier way to get grass than leveling up for a long time just for a chance to get a rare enchantment.
This has been brought up several times in the Minecraft community, and it just sort of makes sense to make it happen. This topic brought up several other conversations of things that could be fixed. The theme of the topic generally deals with entropy – or not allowing mass to be destroyed. For instance, it would also be nice to see blocks reappear after they despawn.
Just so no one is confused, Enderman used to be able to pick up things like wood, cobblestone, and even bedrock, but not anymore due to recent bug changes. But Enderman can still pick up anything else. And that means that these fiends can take diamond and other valuables and they will be gone forever if we kill them while they hold these items. As good as this would be to fix, in an infinitely generated world, this is hardly a major problem.