This post raises several questions.
The Watchtower is distinctly American. As the "American" component of it goes down, what do you think will happen? A Governing body consisting of non-Americans is unthinkable now. The original doctrine is in English. I know the Watchtower has many translators, but, still, that will create a language barrier. What could happen?
What will happen with all those immigrants, in the US, Spain or otherwise, that will have to cut ties with their worldly families? Most of them leave their countries because they want to send money back home. Many have children, wives, parents. Maybe the Watchtower expects those converts to have an influence on their families back home. But, will the influence be one-way only?
I know sincerity is not at the top of the Watchtower's list, but, how sincere would you expect those conversions to be, if a green card is involved? What will happen once those people can stay in the country? They have a supply of instant friends in the Kingdom Hall, yes, but they were essentially willing to be on their own on foreign soil, and they can do away with 150 people. Suppose I have a green card, and a child back home who, I know, won't convert. Will I trade the 150+ for my child? If I do, what will the effect be on my child? Will he get to love the Watchtower?
Just questions.