Many modern missiles are designed to do just that at exhaustion of propellant or loss of primary lock. (whether either or both of these are incorporated in a particular missile depends on what role that missile is intended to fulfil, of course.)
Regarding the OPs points, While I like the concept of the changes proposed, and some of the effects on gameplay would - at least in my opinion - be beneficial, there would be a lot of adverse consequences too and significant portions of the rest of the combat mechanics would also need rework, often to the detriment of the "feel" of ED combat.
I'd love to be able to snipe with a hitscan weapon over extended distances, but how would that work with the scanner mechanics? Even with upgraded sensors at max range you can often pick up a target visually before you can lock them up, and that means you will still have to get closer to resolve their legal/power status and determine if they are a legitimate target. What would happen with railguns? Currently they are hitscan because over the current effective ranges even though their projectiles are not light-speed the difference is insignificant for the purposes of calculating their travel time. If you get out to extended ranges would that then fall into the "forbidden zone" that has as its lower bound the maximum projectile speed the game could track in real time and its upper bound the lowest speed at which the difference between "actual" speed and c becomes insignificant and they can be modeled as hitscan?
With projectiles of any speed not stopping, how far out in the instance should they be modeled? If they were effectively given zero-drag infinite range could you end up with an assault bounty for a cop or clean ship flying through that stream of multicannon, cannon or plasma rounds you missed a pirate with two minutes ago? If it was realistic, you WOULD have hit them, after all...
Ultimately I can't see the OPs suggestions for what I'll characterize generically as "ED guns" as anything less than spelling the total death of the "dogfights and snap shots" feel that FD have often said they were trying to create.
That leaves missiles, torpedoes and mines. Yes they need some work. I can be fully on board with them doing minimal shield damage - if any - as now, but their effectiveness on hull armor is woefully inadequate. They are getting a buff in an upcoming update so I'm ok with waiting to see the results of that before I express an opinion in this regard.
NPC's flying in to your line of fire and getting you in trouble is already a problem. I've expressed multiple times in the bugs section how big of an annoyance it is that I get in trouble for the mistakes of the civilians I'm quite obviously not actually attacking. Obviously a bullet shouldn't ACTUALLY go on forever in the game world, but the limit should be this easy to reach in a game where combat is often reaching the distance of 3 KM just as a result of proper avoidance techniques. I think the ED "feel" is generally very realistic. In fact it feels so real most of the time I go in with real life logic, which is why I'm taken back when my supposed laser gives up after 3 KM. Even after knowing for a while that this is how the game works, I still make that mistake because the game is otherwise so logical. I think more realism would only add to the ED "feel". I'm already sitting smack dab in the cockpit managing all the smallest details of my system and exploring the endless void just like I dreamed of doing ever since Star Wars Battlefront 2. As for the combat they intend: It's great, I love dogfighting, but it gets stale when it's all you do and it's relatively the same every single time. It's the law of diminishing returns. Adding more variety wouldn't take the combat away, it will still be the most basic and readily available option. But now you would have other options, new tactics to explore, unlock, and master. FD has their core dogfighting mechanic and it works, very well. And even the people who opt for different styles will likely be forced in to that basic combat at some point because someone got the drop on them or what have you. But that's no good reason to tell players that's all they're allowed to do when the possibilities could be endless. I'm not suggesting the death of the current gameplay, I like the current gameplay that's why I don't hesitate to blow my money on this game, Horizons is mine the second it launches. I'm just suggesting a sensible evolution of it.