I didn't like this idea when this was originally posted, but it's grown on me a bit. A lot of the time my characters are sitting in out-of-the-way places, waiting for RP that's never going to happen, and that definitely does frustrate me because there's some really cute and cool places in the module that never get used. I think an opt-in would be better than an opt-out, and it would definitely be necessary in my opinion.
I think my biggest concern is forgetting about it; I really do like to think of myself as an inclusive person, but if I forget to toggle off one day, and everyone can see what secret meeting place, or what high-loot dungeon I'm doing, and people decide to randomly show up halfway through RP or whatever and interrupt, I can see it grinding me the wrong way. Preferably it would have to be toggled-on each time you logged in, I'd even go so far as to suggest that it would have to be toggled on each time you change area.