Throwing opinions here, but after working a bit with Shopify themes, there might be some reasons to stick with SSR rather than aggressive caching. First, the storefront can be dynamic depending on visitor region/login/logout. Second, Shopify have most of the logic on the backend, even having non-js html nodes for ordering/add to cart. Third, I don't think the visit distribution of the stores makes caching economically viable (the top 20% store probably don't account for +60% server load).