There are two ways to look at this. If you feel that it is important enough that the system allow logins to occur before it is finished booting, feel free to submit patches, someone might be interested in championing that work.
However, as has been noted, FreeBSD's startup time (even with ports) tends to be under a minute after POST, so I doubt that many people are interested in changing the behavior. Personally, I like to be able to rely on the fact that the system is fully up and running by the time I login.