There's no technical reason they can't do mini jumps, and as far as I am aware the hyperspace cinematic is fixed in minimum length, basically to give the game time enough to load the data for the next system. When you sometimes get extended hyperspace transit times it is due to a slow or dodgy connection, basically you won't come out of hyperspace until the data for the next system is loaded, which is why you get stuck in hyperspace if you drop connection at that time.
Now as I understand they tested in-system mini jumps before beta, that brings up the problem of how to limit it to the stars in the system. You've already broken it away from only exiting at the most massive gravity source, and some gas giants are nearly as massive as stars, and quite often you get stars all through a system, so you end up being able to jump everywhere in some systems. In the end the mini jump testing even had the ability to jump to stations because they were navigation points. In other words secondary stars are at the moment only navigation points, just like stations, planets and asteroid fields, so if you allow mini-jumps to stars it also goes down the chin to other navigation points.
Yes you could add in some more complex stuff to limit it stars, more stuff for bugs to creep into, however it was found to be not a very engaging gameplay. Jump to system, jump to station, auto-dock, turn in missions, cargo etc, rinse repeat. people complain all the time about exploring being repetitive gameplay, jump, scoop, jump scoop. I suspect all you do by allowing in-system mini-jumps is adding more of the same for cargo missions. Oh just to add I don't subscribe to exploration being boring or repetitive, but I do a lot of things apart from jump scoops while I am exploring.
There are going to be differences of opinion on this, just as there are about every other single thing FDEV implement, but implementing every single player request I have seen would be a disaster of epic proportions, of that there's no doubt. I think we need to give FDEV the benefit of doubt, maybe they actually know what they are doing and don't do certain things for very good reasons we don't know, understand or in some cases accept.
As for the last sentence, there is something called "communication". And developers of any game would be forgiven many things if they bothered to communicate with their player base. This especially applies to Frontier, because they are notoriously very bad at communication.
To me in-system jumps between all navigation points do not create any gameplay problems. It also makes sense logically. Your navigation computer is able to give you a travel solution allowing your ship to jump from star to star between various systems. You can even, if you wish so, do minuscule jumps, like 1LY or so (I wouldn't bet there are no star systems closer than that, but I know I've done jumps of 1LY or not much more). There is no logical reason why it wouldn't be able to plot your course over smaller distances. So I would be in favour of a solution like in-system jump or FSD boost (acceleration and deceleration taking seconds, not minutes or tens of minutes).
You say it would make gameplay not engaging... There is absolutely nothing engaging about the current in-system supercruise travel anyway. USS? I ignore them, unless there's something particular I'm looking for. Other than that, I seldom check the descriptions of them (because I need to select them, slow down, change my course - this all when I typically have a destination I'm going to). I check particular ones when looking for engineering materials, such as Core Dynamics components - and this is a good example of situation where supercruise travel is necessary and feels like it makes sense.
Now, if there were some sort of anomalies (a comet, for example. Or a megaship. Or a new station en-route to it's final destination) showing up in my Nav panel after the system scan, I'd be more inclined to check them out. But it would have to be something that allows me for more interaction than scooping some cargo left behind. With this in mind the whole rescue mechanics (which is just scooping stuff in space) - new section in the space stations, that was a move into a good direction. So here's hoping they expand on that.
When it comes to being interdicted, every ship I fly has teeth. I may not be interested in fighting some combat fitted FDL sent after my passengers because it's time consuming, but these are generally not something I have to be afraid of. In most cases the interdiction for me defaults to two solutions: submit and destroy or submit and jump out.
So again, what I'm saying is that in-system travel is not engaging anyway. Hence my proposition: let's do the in-system jumps / FSD boost and please give me a good reason to fly around in supercruise. Engaging gameplay has to, by definition, involve engaging gameplay. More ways to interact with objects in space, more reasons to interact with objects in space, more meaningful interactions with objects in space. As I've mentioned, rescuing black boxes and escape pods was a move in a good direction. We need more of that kind of stuff, dealt with through missions mechanics and building working relationship with powers that be. Go and look for a lost vessel, go and escort new space station en-route to system X, go and deliver parts they need to fix it, go and obtain physical samples of comet on its way through system Y, go and explore derelict megaship in one of the systems in region Z... These all could be very viable reasons to travel in supercruise and look for stuff. Make me care about it and I will happily supercruise many times the distance to Hutton Orbital.