What is mission difficulty? It is a question but I'll answer it myself so you don't have to.
If I'm flying an Aurora and I accept a high-paying mission to transport several hundred SCU then I would expect that mission to be very difficult for me. If I'm flying a Type-C transport then perhaps the missions is just a petty diversion.
So what is mission difficulty?
Some have mentioned risk or loss? Well, low-paying or high-paying is irrelevant if the mission happens to be in a dangerous area ... stuff happens anywhere.
Saying that a difficult Outlaw mission will take place in UEE space is a bit misleading. If the mission is to intercept an escorted ship and bring back the contents then I'd say that was a mission fraught with difficulty. And if you are in a poorly appointed fighter then it is even more difficult due to possible confrontations and SCU transport limitations
So as I see it, a whole raft of missions will be offered. Those who reach beyond their grasp will say that the mission difficult and risky. Those who pick the easy milk-run missions will say they are not too difficult at all.
So it all boils down to the player: stupid, smart, gambler, desperate, swashbuckling ... that is the difficulty / reward system. At least in SC a3.0.
I'm steering the conversation away from risk / reward as that implies space zones. Yes, there are zones but a smuggling missions already incorporates that in the title. The difficulty is in type of material and volume. A pirate mission already implies conflict. The difficulty is in subduing an objective.
So I'm saying that the harder the mission then the greater the reward. Difficulty / reward, not risk / reward. Rewards should be everywhere, logically placed; not placed in bait-like zones.
That's how I see it at the moment.