Basically, the user programs are so good that the priority to implement one went down much lower in the priority list (behind things like improving communication, giving you a 90% increase in your availiable RAM, etc). The nice 3D grapher from Han is *much* faster then any other built-in 3D grapher on any handheld calculator - and more capable in several areas as well!
Please be assured it is still on the list of things to get done, so don't be surprised if it shows up sometime. Note that I cannot give any promises that it will, nor a time estimate of when it might. It is still on the list of things to accomplish however.
Although I work for the HP calculator group as a head developer of the HP Prime, the views and opinions I post here are my own.