For me, the heists seemed like one of the most appealing features of the GTA Online mode, but since the release of the online portion of GTA, there has been delay after delay, forcing Rockstar to push back the release of heists for a long time.
One of the main reasons why heists for GTA Online were delayed for so long was due to the large amount of hackers that entered their way into the game, and this caused Rockstar to refocus their attention on exploits that many hackers were taking advantage of.
Since then, Rockstar have been working on filling the new gen ports with as many new features as possible, and this has understandably left the GTA development team to put even less focus on the GTA Online heists.
Luckily, Rockstar have addressed the online heist delays, and they have stated that heists for GTA Online should eventually be released for the game after the release of the new gen ports.
Considering that the PC version isn't being released till January 2015, we can safely say that heists for online should be put into the game at some point in the first quarter of 2015.
We hope that this is the case because everybody has been waiting for heists for a long time, and the waiting has been killing us.