Great milestone from the SharePoint team: Users quickly create sites connected to Office 365 Groups

Do this Q&A at the bottom of the blog post answers your question?

Q. What happens if my company already built a custom site collection provisioning solution?
A. If you have built a custom site collection provisioning solution, you will be able to maintain it when you select the Use this form at this URL: checkbox. We are working on updating SharePoint Patterns and Practices (PnP) guidance so you can provision a new, modern team site connected to Office 365 Groups (instead of a classic site)—you will be able to programmatically do one or the other per your requirements.