I just called Verizon. The girl said I am eligible for $50 NE2. I asked her to specifically look for the "3g to 4g upgrade $100". She found it, said yes I am eligible, and yes they are combinable. Yes she made a note in the file so when I get to a store they will see it. We did not discuss any particular device. I am currently using a DX.
She read the program rules. It specifically states that a device purchased with this discount *cannot* be later moved to another number in the family. She went to great lengths explaining that I would not be surprised. This discount is only for the primary line on the account. You cannot later switch that device to another line even on the same account. Honestly I don't know how'd they stop you later, but that's what the rules said.
Assuming the GN is available before year end, I will be getting one for $149!
edit: I am in Elmira, NY. We do not have 4g service.