> I could see shopify setting up a system of letting sellers buy a certain original product from a manufacturer - and sending it to some warehouse and selling it on their aggregated store.

Isn't this just dropshipping (already an extremely popular behavior on Shopify). The aggregator I'm describing is one where the aggregator is just solving product discovery, but limited to non-Amazon storefronts, ideally limited to the product's owner, even if white labeled (doesn't entirely solve the quality issue, but would help with explicit counterfeiting at least). A core part of the value prop would be that it gives you direct access to the seller (some of whom may explicitly not list on Amazon) without Amazon as an intermediary.

Google kind of does this, but one of the reasons people go to Amazon is they know the entire SERP will be products, so if they're ready to buy, it's often the fastest way to get to place where they can click "Buy". The aggregator I'm thinking of is really a more aggressively curated, non-Amazon version of this.

Product search is about more than "discovery". You need to categorize products to distinguish variations like size and color. That requires real human curators and a revenue stream to pay them.

Categorization is very possible without human curation, particularly if you're ingesting structured data (as would be likely in the case of a Shopify site aggregator/search engine). And the idea wouldn't be for this to be non-revenue generating, it would generate revenue via revshare on purchases or ads.