That would take away the whole purpose of jobs.
A job is to give all people of the whole community a change to participate in helping build the world, If we would limit this to only a certain amount of people we would be exluding some people and it would take away help when needed.
Limiting it to one world as you mention is also not really practical, if a job needs to be done on main map you're not gonna copy your whole area to, e.g. plotworld, to copy it back to main after the job. (that could also ruin specific blockvariants, like for slabs and boulders etc.)
Also like Eriol and Drao already explained it's not logical to run your jobs on your own in your trial periode, where you want to have feedback on how you did your job and possible improve for your next one.
So i don't really see the purpose of having a job badge, if you want to run jobs, go for foreman