You wouldn't need to do much more than put a pretty front-end on (free|open)BSD to have a decent consumer router.
You can even do this with commodity hardware: http://rtfm.net/FreeBSD/ERL/
Some benefits over linux (this is especially geared to openbsd):
The main reason BSDs are awesome: `pf` is an amazing firewall/routing/shaping system.
Stability: BSDs have been far more stable under heavy loads than Linux.
Security: Generally (free|open)BSD are far more proactive with security patches and fixes than Linux distros.
Because Verizon and others have conditioned people to pay a monthly fee, but they don't back that up with any updates for software or hardware, there should be an opportunity to offer a better substitute.