I don't think having 'untouchables' in open would be a particularly wonderful idea. Yes, it would permit those who do not wish to be involved in PvP activities the freedom to come and go as they please, but in the same breath player piracy is removed, BGS manipulation / PP tasks will be able to be carried out with impunity (not saying that the same doesn't happen in PG/solo - but at least it is 'invisible') and any player bounty hunter could 'see' his target and be unable to act...
No, PG works very well for non-PvP (or even specialised PvP) play, solo is truly player invisible...
If a lack of PvP contact is desired, but some social aspect, remember that system chat is cross modes too...