To have boolean flags in a schema you need to use a text field type and add the truthy and falsy values as a list. This also results in having to have custom models for evaluating from a string value to a boolean in content delivery.
Can we add a boolean field type as a system type with a toggle ux?
It's a simple extension of the system field types that shouldn't take long and fits within the XSD paradigm: http://books.xmlschemata.org/relaxng/ch19-77025.html