i suggest you release the standard features of this referral system to prevent further delays. Just add additional mod-plug-ins for added features. The only main features I see for this mod are:
# Field on registration page that allows a user registering to enter the username of a current user
# Every time a referral is added for a user, their referral count increases
# The board will keep track of who referred who
# User can enter the emails of users they wish to invite via their UCP
# User can keep track of the status of their invitation
* Invitation Sent Status - with an option to send a reminder.
* User Joined
* User is active (made at least 1 post)
* User visited (but did not join) - with an option to send a reminder.
# no permission to simplify this mod.. just a enable/disable referal via global config table
i think this mod already has the main features, i just think that most phpbb sites don't need that "other" features for their site like donate invitations, automatic group membership, etc.
these are just my suggestions... still great mod! keep it up!