What I have in mind is to tweak the max local speed between gravity wells to shorten the middle half of the journey, the potential for existing emergent play is generally at the start or near the end of any in-system transit - make the uneventful part not take as long. Potentially there could be some adjustments to make gravity braking more effective, Ill defer to Darkfyre99's considerably greater knowledge of this area of the game. Big Mike's suggestion for increased speed in trade lanes could work too, provided a skilled pilot could still be faster.
One of the biggest sources of frustration I have with topics like this that people keep on using Newtonian terminology, such as speed, acceleration, deceleration, and so on, when most of what's
actually going on in the game are actually the effects of mass lock: the effects of mass lock on FSD performance, decreasing mass lock, increasing mass lock, and so on. Someone at Frontier Developments, back when FD actually
cared about verisimilitude in this game, seems to have sat down and actually created a coherent model of "Witchspace Physics," one that can be used to explain almost everything about how our ships perform in the game, including Supercruise.
Someone posted earlier in the thread that they tested "acceleration," from 0 to about 2000c at about 20 seconds. The fact of the matter is that it also takes about 20 seconds to go from 0 to 200c, or 0 to 20c. The FSD
always takes about 20 seconds to reach full output, and thus full "speed". It's also why the "6 second" rule works regardless if you're approaching potato moon, a gas giant, or even a star like Proxima Centauri: FSD performance is relative to mass lock, as opposed to an absolute value. It's also why tweaks to mass lock can have counter-intuitive effects:
increasing mass lock slightly decrease travel times of optimal routes while increasing times for non-optimal routes do to braking maneuvers being more effective, and vice versa.
The kinds of "tweaks" both you and Big Mike are proposing would pretty much require Frontier to scrap Supercruise as it is, and rewrite it completely, because presently Witchspace simply doesn't work that way.
My preferred solution to the "problem" of "long" Supercruise times would be optional modules that would, when activated, affect local mass lock: one module would decrease local mass lock, and another would
increase it. Think of them as a "booster" and a "parachute" for your ship, that would also affect
other ships nearby
. Because the modules affects nearby space, rather than your ship
directly, a fleet would only need one ship with a module installed if they're flying in formation. Increasing local mass lock would also be a way for players to enforce blockades or for pirates to ensnare prey.