What is God waiting for before He ends the world?

Oh, there is still some stuff that sould be fufiled before the End of times.

Before the Judgement Day could happen, there must be 144,000 people sealed from all tribes of Israel who were the servents of God. 12,000 for the 12 Tribes.

The devil was the first creature / agent of free will to question the sovereignty of God. God has given the devil time to attempt to prove that agents of free will do not need God in their lives. This time is given because God is righteous. God could have killed the devil but then the question of sovereignty would still be on the table being that the entire heavenly body is witness to these events. So by allowing the devil time to prove his point God continues in his righteous nature. Nothing however will ever work and the devil is ultimately doomed as mankind was designed to have God in our lives and we are designed to live the way he has ordained. No other way will work.

I personally believe the end will be closest once the devil has had the time to try a one world goverment without the presence of the church. In these dark hours, because by then we will have almost destroyed the planet with pollution and the love of the greater will have finally cooled off. That is when god will shut the book, so to speak, on the devil and end the question of sovereignty once and for all

The obvious converse to your observation is that the longer God waits, the more people will be saved as well. That alone could probably justify it, but in addition to that, I'd point out that there are still plenty of prophecies left to fulfill.

To choose just one of the more obvious ones, even with all the turmoil in the Middle East, we still haven't seen Jerusalem besieged as part of a war that drags on for three and a half years, during which time Israel manages to hold out due to heavy doses of divine assistance provided by two prophets living among them...

God is waiting for the fullness of time, a time when all the appointed righteous have been saved.

Until that appointed time, God is being patient:

2 Pet 3:3 ff

3 Above all, you must understand that in the last days scoffers will come, scoffing and following their own evil desires. 4 They will say, “Where is this ‘coming’ he promised? Ever since our ancestors died, everything goes on as it has since the beginning of creation.” 5 But they deliberately forget that long ago by God’s word the heavens came into being and the earth was formed out of water and by water. 6 By these waters also the world of that time was deluged and destroyed. 7 By the same word the present heavens and earth are reserved for fire, being kept for the day of judgment and destruction of the ungodly.

8 But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day. 9 The Lord is not slow in keeping his promise, as some understand slowness. Instead he is patient with you, not wanting anyone to perish, but everyone to come to repentance.

I believe that the best that we know is that He's waiting for the perfect time. According to Romans 11:25-27 though, we know that He will not return until "the fullness of the Gentiles is come in."

"I do not want you to be ignorant of this mystery, brothers, so that you may not be conceited: Israel has experienced a hardening in part until the full number of the Gentiles has come in. And so all Israel will be saved, as it is written:

“The deliverer will come from Zion; he will turn godlessness away from Jacob. And this is my covenant with them when I take away their sins.”" -- Romans 11:25-27

As far as "Wouldn't it be better if God ended the world now?", I would only have to ask "How do you know what's better?" You could say instead of "more people are going to hell" that more people are given the opportunity to choose not to go to hell.

Unfortunately we just don't know. Many people have tried to figure out when he will come back, or what conditions are required for him to return, but quite frankly they aren't specified and we are to be ready for his return at any moment.

Matt 24:35-37 (NIV)

35 Heaven and earth will pass away, but my words will never pass away.

36 “But about that day or hour no one knows, not even the angels in heaven, nor the Son,[a] but only the Father. 37 As it was in the days of Noah, so it will be at the coming of the Son of Man.

Honestly there is no telling when he will come back, but I can guarantee that no one will expect it when it comes: Matt 24:41-44 (NIV)

42 “Therefore keep watch, because you do not know on what day your Lord will come. 43 But understand this: If the owner of the house had known at what time of night the thief was coming, he would have kept watch and would not have let his house be broken into. 44 So you also must be ready, because the Son of Man will come at an hour when you do not expect him.

All this to say we don't know when or under what conditions he is coming back. In fact its pretty clear that we cannot know and that we will not be expecting him.

As to the second half of your question, God knows what he is doing. Even though more people are going to hell every minute that the earth continues to exist, more people are also coming to Christ and more people are being born who will become followers of Christ. You are looking at the pessimistic side, but look at the good side God is saving more people every day the world continues to exist.

I think a good reason lies in 2 Peter 3:9 NIV

The Lord is not slow in keeping his promise, as some understand slowness. Instead he is patient with you, not wanting anyone to perish, but everyone to come to repentance.

Some say that God won't return until all peoples of the earth have been reached by the gospel. As far as I know, all peoples of the earth have not yet been reached by the gospel -- there's still a few left.

In addition to this, I agree with Mason Wheeler that there are still prophecies to fulfill. There are a lot of them in the Book of Revelation. Still, there are a lot of different interpretations (e.g., will the rapture occur before the tribulation or the other way around?) and I don't have any particular knowledge in all this. However, I am sure that we live in the last of times.

Actually, the Bible does have quite a direct answer to the question What is God waiting for?

And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.

Matthew 24:14 (KJV)