For starters, though, I'd like to see a significant reduction in "needless" interdictions-by allowing ships to be scanned (via KW & Manifest Scanners) whilst still in Super-Cruise (with an ability for scanned pilots to be able to try and prevent scanning from being completed).
The likelihood of being scanned-by various NPC types-would depend greatly on System Security & System State. In Medium & Hi-Sec systems, you're much more likely to be only scanned by Bounty-Hunter & local law enforcement. In Low-Sec & Anarchy Systems, it is Pirates & other common criminals who are most likely to scan you. Either way, unless you have something specifically of interest to them, there is next to no chance that you will be interdicted-regardless of System State/Security.
That said, System Security level should effect the base # of scans-& resultant interdictions-you are likely to face, though I believe that Notoriety should be a pretty big deterrent to NPC's in Anarchy & Lo-Sec systems. It should also be a determinant in how difficult said interdictions are to evade.
As far as environmental dangers, I am all for that but-as much as possible-I'd like to see a "Risk Reward" system in place. For example, different types of stars should have different levels of "instability", meaning that their coronas could erupt at a moment's notice, causing severe damage to your ship (though these areas of instability could be ascertained via Surface Mapping, & a potential eruption would trigger alarms on your ship). The reward side of the scale would be that these regions of instability would allow for faster refueling via fuel scoops. Another potential "risk-reward" situation for stars could be that speed & angle of attack could effect scoop speed.......but at the risk of physical damage to the ship if you maneuver incorrectly.
I am sure other posters here could come up with other environmental risks that could be beneficial if used correctly by skilled players.