I think our repsonse to this question depends on individual interpretations of what "big field" means.
If one supposed that the question was asking whether we might see the 1.3 billion Chinese converting to the JW religion, the answer is blatantly obvious. NO! That is impossible. JWs will always be the minority in ANY country, let alone the most populous in the world.
But I interpreted that the question was asking if JW evangelism will thrive in China. And my answer to that is "Yes".
A government's hostility to a religious sect does not necessarily kill it. JWs thrive in Singapore where they are banned. They thrived in Indonesia too (the ban was lifted not too long ago). Need I mention the countries that were formerly the USSR?
And look at Falun Gong indeed! Have they been wiped out yet? NO! Sure you can decimate a good chunk of their members, but the greatest threat to religious zeal is not the edge of a sword, it is information. And that is another reason I am confident that China would be a good land for expansion: little is known about JWs. The same factors that drive the people to embrace Catholicism and the Protestant groups will aid the WTS in making inroads within the Chinese people.