The new disenchanting option in the default loot systems is interesting. Coriel is an enchanter, so it's always available whenever I do a random heroic.
In general, I like the option when doing random heroics. It's very convenient, and it saves me the trouble of handing out shards at the end. I'm somewhat sympathetic to those enchanters who feel it has taken away the profitability of enchanting, as they're probably correct. But I don't really look at professions as a means to make money, so more convenience for me is more important.
It's an interesting change, as it was a game system change that was driven by a social behavior. Enchanters were gathering unwanted items and handing out shards at the end of runs. Blizzard didn't really make this change for gameplay reasons, but to preserve a emergent social behavior that the playerbase had agreed to. This seems like a rare move for them, and I wonder if there are any other examples of social behavior that was later codified into game law.
However, I don't think the DE option is perfect. In fact, I think that the Disenchant Option should be disabled in the Group Loot system.
The DE Option is perfect for random heroics because of the forced loot system and transitory nature of the groups. You can't really trust the enchanter to stick around and hand out shards. As well, since you can't trade permanent items cross-server, the downside to accidentally DE'ing an item is low. After all, you can just run more heroics.
However, in other situations, I think the chance of making an irreversible mistake with the DE button is too high. Let's say you're in a raid that wants to use Group Loot with a "Need for main-spec, Greed for Off-spec, pass otherwise" rule. Right away you can see that someone accidentally hitting DE is going to cause problems.
It's especially annoying because Blizzard allowed Bind-on-Pickup items to be temporarily trade-able to other people in the raid. That made loot distribution a lot easier, because you could recover from mistakes. Did Deborah the Death Knight accidentally roll need on a caster staff? No problem, just trade it to the right person.
But the DE button cuts against that. It allows people to make unrecoverable mistakes with loot, which leads to drama and GM tickets. Simply disabling the DE button in Group Loot would eliminate all those problems. After all, you can still disenchant items manually if necessary.
To sum up, the Disenchanting Option is a good fit for the Need Before Greed system used in Random Dungeons, but it is not a good fit for the Group Loot system used elsewhere in the game.