I've got pfSense[1] running on a passively cooled embedded board[2]. I then use whatever wireless APs I want in bridge mode.
I like this because x86 will always be compatible with anything I might run in the future, and changing out wireless hardware from 2.4 N to dual-band N to ac has been trivial and required no thought to compatibility.
One problem with a "customized distribution" is it probably gets far fewer security updates, much slower, of FreeBSD, than just using straight up main line "real" freebsd.
This kind of logic is why I use plain old Debian as the OS with roughly the same hardware architecture as your design.
While you're absolutely right, this is my home network, and not that big a deal. I'd guess that even outdated FreeBSD is way more secure than most consumer router firmware, which hopefully makes me a less appealing target.
I like this because x86 will always be compatible with anything I might run in the future, and changing out wireless hardware from 2.4 N to dual-band N to ac has been trivial and required no thought to compatibility.