There doesn’t seem to be a specific “release date”. They will appear when they appear . Initial supplies might be limited. Some stores might not even want to stock the 4 GB, since it is so close in price to the 8 GB. Many stores never stocked the 2 GB Clip+.
Even though you have a 16 GB card, I still think it makes sense to get the the 8 GB Fuze+ rather than the 4 GB one, although I personally prefer an 8 GB Fuze to an 8 GB Fuze+.
