The xjc program should generate Java classes which meet the requirements/expectations of the JLS Chapter 13 for binary compatibility , Java Object Serialization Specification Section 1.10 Serializable Interface , and Serializable Interface  which includes the following quote:
"...it is strongly recommended that all serializable classes explicitly declare serialVersionUID values, since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations, and can thus result in unexpected InvalidClassExceptions during deserialization. Therefore, to guarantee a consistent serialVersionUID value across different java compiler implementations, a serializable class must declare an explicit serialVersionUID value. It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible, since such declarations apply only to the immediately declaring class--serialVersionUID fields are not useful as inherited members. [sic]"
Since there is a global variable which allows for serialization, it should be compliant with the intent of providing the API user, classes which meet the expectations of the interface definition.
Please reconsider having end users create a piece-meal solutions which should really be a part of the xjc application itself. As an API user, I should not need to concern myself with low level details that should be a part of the auto-generation mechanism.