Is cortical magnification in the visual system related to synaptic pruning, or is it a separate developmental or learning process? I'm primarily interested in learning about current computational models that explain cortical magnification in the visual system.

With this in mind, my specific questions are: (1) Is this phenomenon a result of the synaptic pruning that takes place in the early years of development?
(2) If not, is it a separate "learning" process along the lines of the hippocampus enlargement in London cab drivers?

I would personally like it if the answers were (1) NO (2) YES, but I'd like to know what the latest science says.
No, it's not due to synaptic pruning. If it were due to synaptic pruning babies would have better vision(esp. Peripheral) but that is not the case. Babies only have better hearing. 

No, it is not exactly a learning process. Most of the foveal developmental starts during the prenatal period and complete by 18 months postnatal.Most of the inter-individual variance have been linked to genetic factors. There is no conclusive evidence for environmental factors affecting the foveal development. But there is speculation for possible environmental factors. 

Reference : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3658155/