There is still an issue with redundancy.
I have two VOIP devices, a regular and a backup, both ringing the same phone and only one of them can be set to E911.
I have a friend who bought a years worth of just E911 from a provider, and is now forced to provide also buy it again from a 2nd when she upgraded from Google Voice. Again one phone two E911 systems only one of which can be active.
Finally a 3rd friend isn't even using her VOIP for phone at all, it's just so her budget wireless alarm system can call her cell allowing her to listen in, turn of the alarm. She can also disabled it/enable it remotely by calling it. There isn't an option to have it call 911.
But rules are rules.