I've seen that this functionality will be included in version 1.4, which will be centered in eliminating the ORO dependency by migrating to Java 1.4. I have two arguments I can think that this may be not the best choice.
1) From the business stand point, we have a window of opportunity that we must take advantage of. I don't personally know how much time it takes to make a new release, but if it is a period such as a month or so for each one, then waiting about two months for a functionality that is already coded doesn't make many sense to me.
2) From a technical stand point, there are many places that will be reluctant to migrate to Java 1.4 for applications that are in production just because of the ISBN thing (though it may be a good excuse anyway) since they are basically just numeric calculations. There are many conservative managers following the philosophy "if it is not broken, don't fix it". Also, the current implementation of ISBN validator uses almost trivial examples of regular expressions, so migrating later to Java 1.4 regexp I don't see it like a big problem (as it could be the email validation code that uses specific Perl semantics in the regexps, then making it more difficult to migrate).