Looks like this limitation is coming from the commit:

"AS7-5135  make sure that the node identifier is validated to make sure nodeName.getBytes().length is <24"

https://github.com/wildfly/wildfly/commit/1fe37204d519bce871219b729b2c78df03f2711f

Exact line is as following:

    public static final SimpleAttributeDefinition NODE_IDENTIFIER = new SimpleAttributeDefinitionBuilder(CommonAttributes.NODE_IDENTIFIER, ModelType.STRING, true)
            .setDefaultValue(new ModelNode().set("1"))
            .setFlags(AttributeAccess.Flag.RESTART_ALL_SERVICES)
-            .setAllowExpression(true).build();
+            .setAllowExpression(true)
+            .setValidator(new StringBytesLengthValidator(0,23,true,true))
+            .build();

AS7-5135  make sure that the node identifier is validated to make sur… · wildfly/wildfly@1fe3720 · GitHub

This is limit that is enforced by JTS system.

that id is included in Xid that is defined by XA spec: http://pubs.opengroup.org/onlinepubs/009680699/toc.pdf

and as Xid has fixed lenght, we cannot have bigger ids embedded in it.