Note: I work in the payments space.

Shopify is one of Stripe's largest customers and a very heavy influencer of their roadmap (example: Stripe Treasury, BillPay (coming soon!), and more!)

Not yet. Still stripe. I assume their eventually do it as they seek larger merchants that will require interchange plus billing and not blended.

ShopPay is 100% a thing.

Shop Pay by is powered by Stripe

Still uses stripe.

Shopify Payments is a Stripe wrapper.

Untrue. They use Stripe.