I am interested in what you said about a "fork-ball"; I do not believe I have ever seen a fork-ball pitch. How is it different that a split-fingered fastball pitch(which I have seem)?
I hope you are right, in that the knuckle-ball will be back - to me it is amazing to watch someone pitch that style and have control of it. To me, a pitcher that can throw a knuckle-ball effectively, is on a completely different level of pitching then most pitchers in the Major Leagues.

The forkball is thrown with the fingers spread over the ball and the ball buried/stuffed into the space between the fingers so there is no gap. Much like PANatsfan's diagram. The split-fingered pitch is very similar, but the ball is not jammed into the fingers as much -- there is a slight gap between the ball and the base of the fingers. I have the DVD set from the 2005 World Series, and in the broadcast for game 1, the broadcasters do a detailed explanation of this with video and still photography comparing the deliveries of Jose Contreras, who threw a forkball, and Roger Clemens, who threw the split fingered pitch.
I think the reason why the knuckleball is a lost art is that kids don't have the patience to develop it, and neither do coaches at the developmental levels of baseball. A poorly thrown knuckleball will flatten out and be nothing more than a fat change up. A high school pitcher, for example, trying to develop a knuckler could be bashed around quite a bit if he wasn't completely on his game. Plus, because the ball is gripped so differently, if your pitching repertoire includes standard pitches like the fastball, curve, and change, unless you have practiced hard to make your knuckleball delivery look exactly the same as your other motions, the use of the knuckler will be telegraphed to the batter.
Here is a video that tries to explain:
I actually think the best place in a modern day rotation for a knuckle ball pitcher is short relief, but not the closer. Charlie Haeger used to be in the White Sox system, and did a variety of short stints with the big club. I saw him come out of the pen to face an innings worth of hitters once, and completely baffle them. Of course, he followed a hard throwing fastball pitcher, and was replaced by the same. The change of pace could be quite effective.