I would like to see a plugin developed for members only Elgg websites.  When a member registers for an account, they must first pay a membership due in order to gain access to the community.  It could either be a lifetime membership which is paid once, or a yearly membership subscription.  Membership dues may be accepted through PayPal, or by other means. 

I think that this would be really useful for other users who are working on a really specific type of community.  Or, for existing membership based organizations.  For example, I could see this being used for many existing membership based special interest groups that already require annual membership dues.  And it would be a really great way to get more organizations to use Elgg.  For example, if the Captain America fan club knew that all they had to do was to install a version of Elgg and they'd be ready to go with their club, then I think that more organizations would be apt to using Elgg in the future.  

Any idea?