WoW Insider posted yesterday about one PvE loot-related hotfix that didn't make the main list for the most recent server restart, and now we have another to inform you of. Blizzard Community Manager Rygarius posted the following over on the official forums:
We agree and feel that Titan Runestones drop too rarely. We are going to make some changes to Lei Shen.
For players that are on the legendary quest line, Lei Shen will now always drop a Titan Runestone. This is similar to what we did with rare drops in the past and will help players that have been experiencing really bad luck.
This change is still undergoing testing and is scheduled to take effect next Tuesday with the raid resets.
Keep in mind that this Titan Runestone 100% drop chance is in addition to the drop chance from all the other bosses, so it's not simply a case of farming Lei Shen for the number of Runestones you need. You could get lucky!
What's not clear is whether Lei Shen will drop one in both LFR and normal/heroic raids, so whether players could guarantee two Runestones a week by killing him on both difficulties. It seems relatively likely that that might be the case, but that's no guarantee.