Description of problem: Anaconda requires that ethernet cards are either given an IP or set to use DHCP. In some configurations like PPPoE you don't actually want to give the NIC any address. redhat-config-network allows this. Not sure what the best way of fixing this would be, one possibility would be to move network configuration into firstboot, which could just use redhat-config-network, but this has issues as well. Or maybe allow a no IP setting (possibly warning that it usually doesn't make sense), possibly explaining that to configure PPPoE you need to use redhat-config-network after the install is done. I assume PPPoE support in the installer is out of the question so I'm not even suggesting that :-)
This is going to be something we need to ask about in firstboot as you guessed.
We can't move all network configuration into firstboot because anaconda frequently needs network information in order to do network installs.
I think the best solution is for people who need to configure PPPoE to just run redhat-config-network after the installation.
Fair enough, as long as there's a way to skip that dialog (and end up with no network at all) vs. the user having to setup a configuration he doesn't want in anaconda just to get through the install. I believe this is the case, but best to be sure...