Currently, bad behavior is dealt with by non-sysops reporting it to a sysop, who blocks the offending user. I propose an extension to allow non-sysops to block particular people they don't want to hear from, from contacting them (without blocking them altogether from contacting anyone on the wiki).
In social media, a more decentralized approach to dealing with bad behavior is applied, in which users can block each other without getting a central authority to block the other user altogether from the site; maybe it could work in the wikisphere too.
Of course, the difference is that in social media, people tend not to interact unless they make the initial decision to friend each other; and by default, communications from people one doesn't know, and with whom one has no mutual friends, tend to go to a spam folder. This proposed extension might make more sense if other social media aspects, such as friending, were more widely applied in the wikisphere.
Going off on a tangent: if spam folders existed in the wikisphere (rather than everything going to either the recipient's main email inbox or to his talk page), it might be possible to relax the rules against canvassing. This could combine well with a mechanism for users' having the ability to block canvassing altogether from certain users. Some canvassing is useful, and some users might want to receive it, while others would prefer to keep it out, or at least keep certain canvassing out.