Not sure if I will be correct about this but I might as well try for a third correct prediction about Shopify:
* Fulfilled by Shopify (https://news.ycombinator.com/item?id=18524131)
* Shopify POS (https://news.ycombinator.com/item?id=6289827).
I'd say it wouldn't make sense to do this. Shopify has no relationship with the retail customer. To build it, they'd have to build traffic from scratch. They'd have to not only build a unique customer brand, but also have to figure out a way to drive traffic, which would likely be through aggressive marketing (Facebook / Google ads), which wouldn't be economical. Secondly, what would Shopify build a brand around for customers?
Amazon's brand is built on the promise of not only providing the cheapest prices, but also the convenience of 2 day shipping (achievable only through scale), amazing customer service (and lenient refunds, again achievable only through scale). This being said, what would Shopify's "brand" promise be?
Curation of their favorite products? Who says that Shopify is qualified to curate?
All of these factors make it hard for me to believe that they'd enter and create a serious business from a unified e-commerce site that'd compete with Amazon.
One large issue that I see is that Amazon wins 40%+ of ecommerce because shoppers searches start on Amazon. Shopify stores lose by default 40% of the time because of that.
Shopify with its huge number of merchants and pre-populated product listings and its centralized cloud-hosted platform is uniquely positioned to compete here in a way that Magento and WooCommerce can't with their distributed install base.
Shopify has to have an angle that is unique to them for sure. I am not sure what that is in terms of marketing. But they have generally done well in marketing, so I trust they will find an angle.
I think the centralized store will be an adjunct to the main offering, thus it will be an option, but because it leads to more sales opportunities, because it helps to solve the search issue, most will opt-in.
I think that they can also somehow tie in the existing stores, of which there are 700,000 into solving the need to introduce people to the centralized search. Maybe if these stores act as a funnel to Shopify's central storefront, they will get click through advertising revenue. Thus the centralization is in effect another revenue stream for stores that refer traffic to the central store. E.g. "If you do not get a sale yourself, at least get the referral revenue on the eventual sale."
I wouldn't be surprised as well (another prediction) that Shopify wants to further own the customer relationship between their merchants and their merchant's customers so that Shopify can market on Shopify's behalf to these customers. I see suggestions of this from the breakdown of the Shopify-Mailchimp relationship. Shopify is working to maintain control of its relationships with merchant's customers.