I love love love builder.io. Just set everything up and I already feel so much more productive than with contentful. The API documentation is amazing. I can't wait to get started with the page builder!
For data models, it would be great if one could make a field unique within the collection. Example: email: unique, referralId: unique so that only one referral account can be associated with the same email and each referral account has a separate referral identifier.