They haven't forgotten about it, they just haven't added it yet. They've stated that, on multiple occasions, when they do finally add it it's going to be more than just simply getting to a new rank and having some crap new gear available to buy.
I believe that we're going to be able to hire Grand Company NPC's to do things with us somehow, be able to command our own little platoon of GC Soldiers :P Doing something that complicated takes time to get it right. In 3.2 or maybe even as late as 3.3, we should hopefully be seeing some info about it.