Any answer to the question hinges on whether one things Jesus is pointing toward the eschaton, or something more immediate. While I agree with those who have stated that the early Christians did anticipate the Parousia to happen in their lifetime (and certain Hyper-Preterists go so far as to say that it did--a whole other set of hurdles to jump over), I'm not at all convinced that Jesus necessarily is pointing toward the eschaton in this point.
While I would argue it is an eschatological statement and is eschatologically relevant, it's not necessarily about the eschaton itself. One of the things I think we see addressed in the Gospels (as well as other places in the New Testament) is a sort of "now-and-not-yet" attributed to God's kingdom.
On the one hand the kingdom means the consummation of history, the end of this age and the birth of the Olam Ha'ba--the age to come. That which the Prophets often pointed toward, using language about turning swords into plowshares and children playing around viper dens without fear of being bitten, lambs and wolves lying together in peace.
Something consistent in the Gospels is the zeitgeist saturating everything at the time, it is a highly politically charged atmosphere. The Maccabean kingdom had been conquered by Rome, there were plenty of apocalyptic texts and a general sense of nearness of messianic liberation which entailed a political overthrow of Roman tyranny and the reestablishment of Israel to its days of glory.
Jesus preached in this atmosphere and "kingdom of God" carried profound political overtones, though Jesus also consistently uses the kingdom to subvert the concept of power and authority present in both the revolutionary voices of the day as well as the authoritarian (i.e. Roman and Roman collaborating) voices of the day. And yet we see that people were really failing to grasp at Jesus' point as late as the moments before His Ascension.
"When they had gathered together they asked him, 'Lord, are you at this time going to restore the kingdom to Israel?'" - Acts 1:6
That is, "Lord, are you NOW finally going to overthrow the Roman powers and liberate us and usher in the time promised by the Prophets?"
The kingdom which Jesus speaks of isn't "of this world", it doesn't resemble the powers and principalities of this present world, it's not the violent revolution which the Zealots strove after, and it certainly wasn't the violent tyranny of the Roman Empire.
The kingdom, instead, looks like the Cross.
The nearness of the kingdom is present in the Person of Jesus, healing the sick, giving sight to the blind, pronouncing forgiveness to sinners, in the transformed hearts of tax collectors like Zacchaeus or that of the woman caught in adultery and in the driving out of demons. Remembering that the kingdom does not "come with observation".
And, of course, by saying all this by no means robs the preaching of the kingdom of its eschatological import. But rather than looking forward to a violent revolution to usher in the age to come, Jesus presents Himself as the Victim on the Cross, crucified for the sins of the world--this is the True King of God's kingdom, this is what the greatest in the kingdom does; be a servant, to be the least. And it radically turns the world upside-down by presenting a subversive and alternative way of looking at everything. Who are the poor among us? Who is the outcast? "Whatever you do/do not to the least of these you have done/have not done it to Me."
Again, the kingdom looks like the Cross. It is cruciform.
This by no means denies the eschaton, the coming fullness of the kingdom in the age to come, God setting all things right at Christ's Parousia. But it does mean that we must understand the kingdom as being not other than the Crucified Jesus, but rather to understand the Crucified Jesus as the radical example of what the kingdom is and looks like. It isn't "power" as "power" is normally comprehended, it's the power revealed in and through the weakness of the Cross, it's grace and forgiveness, mercy and justice. Remembering what St. Paul says, that God chose the foolish and the weak things of this world, and that Christ is the wisdom and power of God.
To that end, I think it is perfectly legitimate to see Jesus as pointing toward this "hidden-ness" of the kingdom displayed on Golgotha. Pointing toward the reality of the kingdom revealed not through a mighty display of eschatological glory, but revealed through the Cross. To witness the kingdom come which puts to death the powers and principalities and dominions of this world through the suffering of Christ on the Cross and the preaching of that Gospel to all nations, beginning in Jerusalem and Judea, Samaria and to the ends of the earth.
Again, I'm simply trying to offer a way of looking at this within the context of Jesus' kingdom preaching which in all four Gospels culminates in the Passion and Resurrection from the dead.
-CryptoLutheran