A few ruminations on the annual report in the February 1 Watchtower (numbers are rounded & approximate - don't jump all over me if I'm a little off!):
If you add up the "population" figures for all the countries listed, you get approximately 4.4 billion. That means that there are about 2.5 billion in the "Other Countries" not listed - primarily China and Islamic countries.
However, there are only about 13,000 JWs in those "Other Countries not listed" to preach to those 2.5 billion people.
Throw in India, with a population of 1.1 billion, and you end up with about 3.5 billion of the planet's population. There are only about 25,000 JWs in India.
So, out of the total JW publisher count of 6.6 million, something like 99.5% of them cover 1/2 of the world's population, while the other half of the world's population only has the chance to hear the "good news" from about 0.5% of the JW publishers.
38,000 JWs have the responsibility to preach to 1/2 of the world's population, 3.5 billion people.
And think about this: The ratio of population to JWs in the US is about 288 to 1 - let's call it 300 to 1 to keep working with round numbers.
In the US, the usual standard is to cover all of a congregation's territory twice each year. Some congregations cover it more frequently, some less, but as an overall average, that's probably about right.
Thus, to cover the territory twice a year, each JW has to talk to about 600 persons (300 to 1, times 2).
So, assuming that ratio holds earthwide, in order for a country to cover it's territory in a year, the ratio should be 600 to 1, or less.
Now, what is the "publisher to JW" ratio for 1/2 of the world's population? 3.5 billion to 38,000, which works out to 92,000 to 1.
If each JW has to talk to 600 persons in a year to cover the territory, how many years will it take those 38,000 JWs to preach to those 3.5 billion people?
92,000 divided by 600 = 153 years!
If a prerequisite to "the end" is a thorough witness to all nations, well, don't cash in your 401(k) yet!