The default bare-bones thin events are sometimes not enough e.g. Blue Ocean needs some additional info about Job events, such as whether or not it's a muti-branch job, the Jenkins org the job belongs to etc.
At the moment, Blue Ocean is fudging this by parsing the job url and making a few assumptions. This is dodgy and we should fix it before we go too far. Allowing BO to define an @Extension point impl that adds the few extra fields it needs would be good because then it would not longer need to make any assumptions.