OS installers should be easy to open up and modify
A while back I tweeted:
Every so often I dream of genuinely sysadmin-friendly OS installers. I doubt I'll ever get them, though.
As it happens, I have a specific vision of what being sysadmin friendly here should be and that is easy modifications.
The reality of life is that OS installers are necessarily very general but they are most frequently used in much more specific situations, ones where you already know the answers to a lot of the questions they'll ask. At the same time there's often a few local questions of your own that are important and need to get answered in order to set up a machine properly, and not infrequently the set of packages that is available on the install media is not ideal.
A genuinely sysadmin friendly installer would be one that fully understood this reality. It would make it not merely possible but easy to open up the installer image, make this sort of straightforward changes to it, put the whole thing back together, and have a custom setup that fit your environment. Want to run a post-install script? It should let you do that. Want to drop some additional scripts and files into the installed system? Ditto. And so on.
(A nice implementation would allow you to ask your own questions within the installer's Q/A framework and then export those answers to your post-install scripts or write them into the system or the like. A really nice implementation would allow you to use these answers to drive some of the regular installer actions somehow, although that gets more complicated.)
Of course I know that this is a quixotic quest. The modern world has decided that the answer to this problem is doing as little as possible in the actual installer and customizing the system after install using an automation framework (Puppet, Chef, Ansible, etc). I can't even argue with the pragmatics of this answer; getting an automation framework going is a lot easier than trying to persuade Debian, Red Hat, FreeBSD, OmniOS, and so on and so forth to change their installers to be nicer for sysadmins (and a full framework gives you a much more uniform cross system experience).
(Debian and Ubuntu have a 'preseed' feature but apparently rebuilding installer images is somewhat of a pain and preseed only goes so far, eg I don't think you can add your own questions or the like.)
(This whole chain of thought was sparked by working with our standard install system and thinking about how much of it could and really should be in the actual installer.)