I'm sure they're aware of a ton of angles this could be abused, and am sure they're prepared for those. I'm also sure that there will be some issues that they don't anticipate, which is also fine because they'll be dealt with.
Let's look at this in a positive light, something that can be introduced and adjusted as needed in order to promote the game, rather than instantly try to pick it apart.
I think this is an excellent idea, provided the monitoring is strict. The rewards are substantial, which is hopefully enough to encourage people to invite their friends in and encourage them to stay. Maybe the initial reward is lowered, with a secondary buff if the newly invited player stays for x time? One month, one age, whatever? That might alleviate some of the concern about people creating multiple provs to abuse huge rewards, but still rewards legit players using the tool as intended, bringing players in AND trying to get them into/staying with the game.