Duskblade of Draktharr being removed in 6.4
The biggest change we're making in 6.4 is that we're removing Duskblade of Draktharr from Summoner's Rift. There are two major reasons we felt we had to do this, so I'll run through both:
First, DoD tends to make burst patterns even more bursty. The item effectively adds another nuke spell on top of kits that are already designed to have strong up-front damage and aggravates the "whoa, I got one shot out of nowhere" frustration of playing against certain champions. A good example is Zed; DoD adds reliability to his assassination patterns and ends up removing counterplay he gets to rely on his Q, E, and DFG spells for damage, and can use dashes to reposition or escape instead of making more risky plays).
The second reason is strongly tied to the first; removing this item gives us room to buff champion kits that would otherwise be overpowered if they could use DoD. The most obvious example is Shaco; more 'assassiny' elements of the character, like his sustained damage or kiting, end up getting washed out because he has so much power to blow up feared targets with a DoD burst. This ends up forcing us to balance Shaco around his mage playstyle because there's always the "I can buy DoD" route to consider; removing the item means we can buff him in more interesting ways while still keeping some of his burst because he can't just pick up a DoD and double down on a single playstyle.
As far as champions that purchase DoD are concerned, some will get some love now that DoD is gone (I mentioned Shaco; expect Talon to get attention either this patch or next); some are strong enough that losing DoD is a healthy nerf; some rely on alternate item builds sufficiently that they won't be affected too much. When 6.4 goes live, if we feel there is an itemization gap for assassins, then we'll address that further.
Oh wait, I meant DFG and I meant 5.2.