In M1, On checkout page there is following 2 option for customer to checkout ,
In Register and checkout there is Password and Confirm password field which is for registering a customer.
I would like to have this feature in Magento 2 when guest checkout is disable. Right now we can't force customer to register while guest checkout is disable.
If this is functionality that all Magento 2 customers are having to pay developers to fix/customise, I would suggest that it is something that Magento should add to its core functionality.