Note: This article is outdated and only works with 2.1 versions, no update yet.
Today I came across the challenge of removing the username field from FOSUserBundle and found a nice and clean solution based on events.
The great news, that ezpublish will use the symfony framework as base for the next major release has spread now for a while and everybody (especially me, as being a ezPublish and Symfony developer) is very happy with this radical change in the develpment strategy of EZ Systems.
But it will take some time, until the new version is stable and can be used in production. Also we will be stuck with all these already running versions where there is no budget to upgrade and migrate the code to symfony. However, some of the symfony goodness can already be used with old ezPublish versions.