Is it possible to upgrade from 128GB PCIe-based Flash Storage on a MacBook Pro 13" with Retina?

I'm planning on purchasing a MacBook Pro with Retina Display. Since 15" is outside my budget, I initially thought of purchasing 13" ret 8GB RAM/256 GB storage but since 8GB is not upgradable (or does not have a slot for another chip) and will require replacement of the motherboard which means more cost, I'm thinking of getting 16gb RAM/128 GB storage.

In the future when I get to have enough savings, is it possible upgrade from 128GB PCIe-based Flash Storage on a MacBook Pro 13" with Retina?

I'll mainly use the device for browsing, downloading, post processing of photos/videos and music mixing. Any advise is appreciated. 🙂