Okay eggy, if 911 cranks really are different from UFO cranks then there's no way we can use the UFO example to predict what will happen to the whole 911 "truth" movement is there? So if we come back in a few decades we'll see that I got all of the following wrong...
The 911 truth movement will never reach a consensus about what happened on 911, simply because all their 'evidence' and anyalses are so obviously mutually exclusive, yet few of them have the backbone to criticize any 'evidence' which appears to implicate the Conspirators.
After being unable to formulate a consistent theory the 911 truth movement will become bitterly fragmented with public disputes between various competing theorists appearing all over the internet.
One or more individuals will come to light who claim to have insider knowledge of the plot or where somehow directly involved in it. They will of course be able to provide no convincing evidence of this. Supporters will claim its because the evidence is being erased.
There will be a number of breakthroughs which will turn out to be hoaxes. But when the number of hoaxes becomes high enough, theorists will begin to claim that they can't all
More books will be written, more 'documentaries' assembled, more money will be made. Yet no living person will be directly and unambigiously accused, let alone brought to trial.
The 911 conspiracy will seep further and further into popular culture but yet be taken less and less seriously, and not make the slightest bit of difference.
As more real information emerges, the theories will become even more desperately convoluted, to the point that no serious 'truth seeker' believes the silly theories that were knocking around back in 2006
911 theorists will reach old age and die, having unearthed nothing of any value, or even gotten into trouble with the law.