All the characters will be given an option whether they show up in the general who or whos list, which will basically be a neutral list. As you meet people, you can grant certain individuals the 'right' to have your name displayed on the who/whos list, even if you toggle it off, for obvious reasons. Chat will be done through voices after skilltrees, so i doubt that will be much of a problem. Also, by grouping with another person, or following another person (other than stalk, after skilltrees), you will make yourself visible to the other's who/whos list, and pking, giving eq, giving gold will toggle this as well (mmm. could be used to hunt multiplayers :P). By joining certain RP clans, you might have no option to this. Of course, saying anything on public channels, come to think of it, will have to force you to toggle who/whos visibility on. Maybe those with this option toggled should, during while they have it off, not be able to say anything over info, but only listen. As far as auction and chat goes, it will be the equivalent of having them off. Tells-wise, you would only be able to receive tells if the other person can see you on the who/whos list, so if you have it toggled off, only your friends or those you grouped/followed/traded will be able to send you tells. This could also easily serve as an RP reminder as well as cross-play reminder.
Mmm...but regardless of how many ppl have toggled it on/off, you should still be able to see how many players are actually online.
Current invis effects should remain the same.