I'm in the same situation. I'm currently with Verizon using a 32gb Samsung Galaxy Nexus. I use my phone equally for work & play, so I've got a great deal of applications, as well as photos, music etc.
In checking out the S4 at my local Corporate Verizon store, I asked about getting the 64gb version, and when it was available. The woman said that I don't need anything more than 16gb, and that I could expand upon that by adding an SD card and offload applications to it. I kindly explained to her that this can no longer be done, and she argued that it could. I asked her to show me, and she said that she had no SD card with which to demo (facepalm), then stuck to her story.
I refuse to believe that Verizon's CSR staff can be purposefully/willfully miss-leading, and that they must be parroting the information that they have been told to feed their customers.
Later in the day I visited my local Best Buy, and was informed that they have no information as to when, but both the 32 and 64gb S4s are coming.
I've got time, so I'll wait until I receive confirmation one way or the other, or find the next "superphone".