In a new post to his PHP::Impact blog Federico Cargnelutti he suggests that the nest "killer app" for the PHP world is something that can (quickly and easily) do database migrations.

Schema synchronization is the killer feature missing in phpMyAdmin! This feature can be found in some commercial applications, like SQLyog Enterprise for example. [...] However, SQLyog DST is not free and only runs on Windows. So, if you want to build the next killer PHP application, port SQLyog's database synchronization tool to PHP and open source it. People will love you for it.

He links to a few different resources including a blog entry on database versioning and an article showing how the synchronizing is currently done with SQLyog.