When you are in the flow or deep into product categories a swipe to go back would be an enhancement of the usability. Phones are too big these days to easily reach the backbitten in the upper left corner.
Being able to navigate us gin swipe just like you can swipe down to refresh the store.
The newly added bottom bar can also help with navigation. The feature came out a while back, and really helps with in-app navigation. Have you tried it out? The option is available in the Settings module.