Exactly....there are simply too many variables.
DTV could easily do this. MLB does it filtering on IP address and they have to do it on a daily basis. The mobile IP filtering doesn't work real well though.
The only way to assure compliance to NFL blackout rules is to be absolute in enforcement. I suspect the DirecTV agreement with the NFL for Sunday Ticket requires it.
So it comes down to home location (only), anything goes (which violates NFL requirements), or something else in between (which is highly complex and costly to enforce).
Like an earlier poster indicated, the safe road was traveled for this mandate.
It would seem to be more worthwhile challenging the actual rules themselves in contrast to those who look to comply with them.