What is the view of Jehovah's Witnesses on John 18:36 "My kingdom is not from this world"? A lot of people don't consider JWs to be Christian, usually for the reason of their view on the Kingdom of Jesus to be a kingdom here on Earth. I respect the guidelines of this site, so I do not wish to discuss who is considered Christian and who isn't. I'm only curious about how they view John 18:36 and similar statements. Despite Jesus explicitly stating multiple times, that Heaven is something totally different from what we can perceive, and is not from this world, they still believe the following two views, which very few if any Christian denominations accept:


The number of people admitted into the "real Heaven" is limited, and already filled.
All the rest have only a chance in the best case to live here in an earthly utopian kingdom, which is not eternal.


What biblical basis do they have for it? Their door-to-door preachers I had seen, neither could say anything except a small handful of Bible verses they memorized, but nothing in this topic. I don't have the occasion (neither do I have the intention) to start lengthy debates with some of their better qualified members, this is why I'm asking here. 

It would be good if someone here was a Jehovah's Witness, who could tell their view on this question. It might even be possible that the two points I listed come from a misunderstanding and they don't really have those views, could someone more knowledgeable clear this?

Of course, you don't have to be a a JW to post an answer :)
This is actually a verse that Witnesses would know well, and quote often. It is on the basis of this verse that Witnesses avoid politics (and, generally, careers which would result in fame). Witnesses do not vote; do not join political campaigns; do not donate to political causes; and do not join political parties. This is all on the basis of John 18:36:


  Jesus answered: “My kingdom is no part of this world. If my kingdom were part of this world, my attendants would have fought that I should not be delivered up to the Jews. But, as it is, my kingdom is not from this source.”


To the Witnesses, Christ's “Kingdom” is not a simple synonym for “Heaven”. Furthermore, “this world” is not a synonym for “planet Earth” or “the physical universe”. In other words, the verse you reference has, to the Witnesses, very little relevance to the beliefs you’re asking about.

“This world” is the current political/social system. Witnesses try to avoid being caught up in it much, as explained above.

“The Kingdom” is God’s system, implying a structured rulership over subjects, living here on Earth in the “new system”. That Kingdom is, in fact, eternal. I don’t know where you got the idea that it isn’t. (It will be briefly interrupted 1,000 years in, but after that it’ll go on eternally.)

Living on Earth is not supposed to be a second-best. It is, in fact, the original plan for humanity. The few who go to heaven to be kings of the Kingdom (“joint heirs with Christ”) are the anomaly.