To be honest, most of what has been suggested are already ideas floating around for RS5.3.
We have been discussing a job level system, along with the ability for medics to heal / revive the heavily wounded. We also have been discussing vehicle engine failure upon too much damage as well. Because I don't know what Rockstar was thinking not to make this a standard feature in the game like it is in GTA 4 and 5. I like the idea of car fires for firefighters, but I don't think it should happen 100 percent of the time. Maybe on a random chance, otherwise the car engine is just dead.
The only thing we haven't considered is accidents / damaging player from vehicle. To be honest I don't think it's necessary if we go ahead with the engine failure script. That by itself should be enough to encourage players to drive more responsibly and roleplay accidents more.
And also regarding fire and EMS, it is a big possibility that both systems will operate similar to the SAPD system, but under the command of SAFD. If that becomes a reality, as it hasn't been finalized yet, medic/fire duty will be like the "freecop/recruit" system of SAPD. Like the SAPD you could apply for ARFD to be formally trained and do more things, and possibly get paid more. It might sound weird combining EMS under the ARFD umbrella but this game is based on the United States, and very many cities and counties here actually combine both fire and EMS into one service. In my area specifically, firefighters are also trained EMTs.