Once I participated in development of such Maven plugin under the same circumstances - migration from Ant to Maven, delta builds.
I think one of the reasons why such plugin doesn't exist in open source (besides conflict with Maven philosophy) is that rules for the assembly of patch (delta) is highly specific to every concrete situation. For example, our patch structure consisted of more than a dozen subdirectories, all with different rules for inclusion in patch, also affected by merges.
However, in my opinion, our decision to write Maven plugin instead of supporting old Ant scripts was right. Testing and support of Ant code is quite expensive, and integration with Maven adds even more complexity. On the other hand, it's not very hard to cover Maven plugin, written in plain Java, with unit and integration tests, so regressions could be caught easily.
So, if you plan to keep requirement of making delta builds, I recommend you to invest time in writing custom Maven plugin.
We used SVNKit library for integration with SVN to simplify development (no need to parse text output of svn log
) and make our plugin environment-independent (no need to have svn
binary in PATH).