The #2 issue Shopify sellers face is fulfillment, but IIRC they are investing $1B+ in building out their own FCs across the US. (Which is peanuts, but a step in the right direction)
I don't see the appeal. I really, really like Shopify as a seller and would always recommend it to someone looking to sell online, regardless of volume. However as a customer I couldn't care less about a Shop's backend as long as I have a pleasant shopping and ordering experience. And Shopify alone doesn't guarantee that.
A general search engine and price comparison for online stores/products, regardless of platform, is more appealing, but I think we already have that, at least here in Germany with Idealo, Geizhals or Google Shopping.
Of course, when Shopify can provide fast, Prime-like shipping with their new fulfillment plans that's an actual appeal worth searching for.