Right now there is no real in game mechanic that limits what I would consider, and regularly argue, as recruitment abuse.
It detracts from the game.
It detracts from the spirit of the game.
When a merge, or mass recruitment occurs, for no other reason or result than removing all competition from the world, it can ruin the world. Interest drops, players quit. It creates a tough environment for newer players. I have seen an atmosphere of players (including moderators) try to shut out, or detract from. the learning experience that newer players NEED in order to survive and maintain interest and learn vital game skills beyond farming in order to thrive.
When a tribe recruits a large percentage of the active player base for a world, it kills the challenge, it kills the competition, and the longer the effect lasts, the more damage it does.
This is a bold move by the US team, to try to urge more competition, fewer cheap victories and bring back excitement to the game. As a bold move, it will be open to scrutiny, and I agree that there needs to be a clarification, but I have never seen this attempted before, so give it a chance, provide your feedback so that this trial CAN be tested, and evaluated, and maybe proved. Clarification will come as the rule is tested and your feedback rolls in.