There isn't a microSD card on either of the Nexus 4 models, so whichever capacity you invest in, that's what you're stuck with for the life of the phone, at least in terms of local storage. Google Drive and other cloud services represent alternative means of saving data.
In any event, the 8GB Nexus 4 is apparently gone forever. The Verge says it was told by Google the search giant isn't planning to restock the device, so don't get your hopes up by the message that reads, "We are out of inventory. Please check back soon."
What this suggests is that Google is trying to purge itself out of existing inventory in preparation for a Nexus 5 launch, or whatever the next model Nexus smartphone is called.