The article Creating a Custom Payment Form with Stripe.js says:
This method of using Stripe.js to collect card information using a custom payment form has been deprecated
When creating a payment form to collect card information, use Stripe Elements—our pre-built UI components.
Check out our Elements migration guide to learn how to migrate your checkout flow to Elements.
Why is it?
I have got an answer from Stripe:
To answer your question, no, the custom payment form technology was not deprecated due to any new PCI DSS rules or regulations. We’ve deprecated our custom payment technology to make it easier for new users to integrate into Stripe and build their own custom payment form.
What we’ve done is add a new feature, that we call Elements, to our stripe.js library. These Elements make it easier for users to create a custom payment form to collect payments from their customers.
This change has no bearing on PCI DSS regulations and should not impact our users as far as PCI compliance is concerned.
The Stripe Elements technology is fully implemented in the 2.2.0 version of my extension.
Previously, it was implemented in the multishipping scenario.