The issue is that mods are not really able to directly affect braking distance. The easiest way to increase braking distance is to increase the weight of the vehicles. A side effect of this is that the trains consume more fuel, and are deadlier on impact with a player.
The core game logic calculates all the braking, based on the current speed, the train mass and the braking power (affected by research).
It's easy to detect acceleration, and reduce it, because you're simply reducing the speed-increase, and then it simply takes longer to arrive.
It's easy to detect deceleration, and reduce it, but that means you'll overshoot your destination. To work around this, it means that you have to calculate (almost every frame) what the stopping point is (either simply a station, or checking all rail-signals along the projected path), and how far it is, what your (calculated) braking distance is, and whether you should already be braking. It's quite tricky to get this right, and has a serious performance impact.
Long story short: it's hard, and slow - and I'm not sure it's worth it.