I have several ideas,
1. instead of a attempted murder why not a real murder where the victim is dead possible ers berlin has it
2. Random vehicle spawn for freeplay like the new york mod has again possible
3. ( not sure if this is possible) two competing riots that you would have to separate and arrest, instead of just attacking your officers the different groups would attack each other. what about one that just starts of really big with people looting like on the mission what your describing sounds alot more like a gang fight
4. A warrant, you would need to go to some person home and arrest him.would need scripting
5. Drug deal where you would have to catch two people who would take off in different directions possible i would think
well i thought about some sea rescues like capsized boat major shooting (gangs) and what about hostage situation but with four people with mp5s or something