I’ve read enough of the MavenPublishPlugin to tentatively conclude that pushing to S3 repositories would involve selecting a Maven S3 wagon, such as is implemented here
https://github.com/jcaddel/maven-s3-wagon
Do I have that about right?
I don’t know how the current plugin selects a wagon protocol, but it could be by-protocol in the repository URL. Repositories prefixed with s3:// would automatically select the S3 wagon. Such a URL is seen here