I tend to think it's some combination of 1 and 5. I think he was stopped either in a car or by a neighbour in the front of their house to help with something with their garage, trash cans, car, etc and was then taken somewhere by them under the impression that they were dropping him down the block to the school to meet the coworker.
Ruling out any of that I'd say possibly something to do with his work.
Bullies or suicide no chance imo. His disappearance has something to do with his routine of that particular day in leaving early for work. There is nothing to suggest he was suicidal at all from what I've read. Or that he was being bullied so severely to the point of harassment.
I don't buy the accident theory either because really how often does that happen? Where someone just runs someone over, the driver throws them in the trunk drives off and disposes of them? Most people panic in that situation and would more likely drive off and leave the body imo. Plus the time frame is so short that someone knocking him down, getting over the initial shock, getting out of the car, picking up his body, cleaning up any mess, etc they would have been noticed by SOMEONE in the time they were doing all that within an open area.
I'm not sure i believe the gang thing either. I have read from some people that the area he was living was the ghetto or on the border with the hood. Looking at where Jason lived on google maps the area looks very nice and suburban and wide open. I grew up in the inner city and where i lived doesn't look anything like the kind of area where Jason was living. Of course appearances can be deceiving and it could have looked different back in 2001, but i just don't find anything to suggest his disappearance was gang related. Where he lived just doesn't look the type of environment where you get robberies and muggings or shootings at 10-11am in the morning. Plus people in street gangs with little organization don't just tend to make random victims or random nobodies 'disappear'. His body would've been found by now.