M0n0wall is succesful in large part due to the vision of its designer. Manuel provided the following guidelines that a captive portal needs to meet for him to consider adding it to the core m0n0wall release (taken from Manuel's email):
Manual also asks:
Did you check that it fits in with the rest of m0n0wall
without requiring a complete overhaul thereof? I mean - you know that
ipfilter doesn't do layer 2 filtering, and that ipfw has got a kinda
"reserved" function for the traffic shaper, which must work no matter if the
captive portal is on or off. Same goes for other functions like VPN etc. of
course.