I have an app idea that I would like to see, and I think others would find it very useful as well.
We work with partner sites. Their customers (who are already logged in to the partner site) will then like to our shopify store. In order to make things easier on the customer, the partner would like to be able to send us the customer's account into (email, user name, password, address, some other metadata) so we can automatically create a matching customer account in our Shopify store.
This functionality is similar to Multipass, which is only available via Shopfy PLUS. But a small shop like ours can't afford to pay for all of the extras that come with PLUS when this little piece is all we need.