Admin report on multiple sessions detected and action taken?

In addition, it would be nice to set the module to passive mode so that it simply provided reporting but didn't take any offensive action against the user. This would be more for monitoring, etc.

Yes this would be great, second both suggestions.
Tentatively upping to Major. :-)
And this would probably be developed on the 7.x branch first, then possibly backported.

There is already a lot of information logged to watchdog which shows when settings are changed and when sessions are limited.

If more reporting is needed then I feel like it's beyond the scope of this module. Perhaps a sub module can hook into the events already produced by this module and store the report in the database somewhere.

Seems like the major change needed here is being able to put this module into a passive mode so it doesn't actually limit anything but just fires it's hooks and rules, leaving the action up to any implementations there.

I don't have a use case for that so can't justify spending the time on it, but if there's a patch to effectively disable the action of this module, it could be interesting and useful.