Hello 
I like this approach a lot! However, it bothers me a bit that the display name cannot be changed before the registration is finished. I think it would be great to add an option to change it during the process.
In my community, I have disabled the Prioritize username in UX site setting, which means the Full Name/Display Name is prioritized across the UI. Because of this, automatically assigned names like “user21” look pretty bad on the front-end if the user doesn’t have an immediate option to customize it.
Thanks!