Is it possible to implement user groups. Let's say there is a group "squirrels". Everybody who has joined that group can be pinged with with @squirrels. It might make sense to make this feature only available to group members, i.e. the ping will only work if the message is from another member of the user group. (On the long run one may need the possibility to ban certain users from a given group, of course I hope this will never be necessary.) 

So the question: is it technically possible to achieve this? If so, do others also see the need for this feature?