[1.9 Advanced Blade Controls]

On 2/12/2020 at 2:59 PM, Maxsimal said:

until we realized that PhysX does not actually simulate precession at all. 

Maybe you can turn that frown upside-down, because my copy of KSP simulates precession just fine. 
I certainly see the 90° phase lag if I cheat a rotocraft into space, and try to rotate the rotor disk using reaction wheels. In version 1.7.3 I made a helicopter with cyclic control with the full 90° compensation for phase lag, so the force vectors on its counter-rotating props appear to cancel each other, but it pitches and rolls as you would expect assuming a 90° phase lag.

The gyroscope effect on Breaking Ground helicopters is extremely weak, because the angular momentum of the propeller disks tends to be unrealistically small, because
1) the rotational motors do not put the angular moment of their drive shafts in the physics simulation; and
2) someone offset the centers of mass of the helicopter and prop blades, very close to their mounting points.

Helicopters made with the Breaking Ground blades have more rotational inertia in the craft body than in the spinning rotor, so the phase lag tends to be very much less than 90°. 

Edit: precession demonstrator in KerbalX (link)

[1.7 Maneuvering Engine Balance Changes]

The high impact-tolerance of the single-port RCS in particular, with its spherical collider, might have had an important side-effect in enabling some creative bearing designs.  There is an interesting niche of use of KSP to make devices with separate interacting craft , often with RCS ports as the teeth of the gears.  When a new-ish player expressed interest in stock propellers last week, I said "there has been a golden age of propeller designs on kerbalx recently."  A niche, but one that gives KSP good publicity.

The risk is that a significant number of interesting designs have parts slide against each other at >15m/s, and KSP seems to treat sliding velocity as collision, so become impossible without mods or 'disable crash damage'.   So far, though, the RCS-using designs that I have tested (link link) work fine in KSP 1.7; I'll update if someone reports a specific affected craft.

If the high impact tolerance is getting in the way of some other use, then it makes sense to lower it.  But we could rationalize leaving it at 50m/s, saying that monopropellant engines are relatively very simple, with a valve, catalyst, and nozzle, so the single-output designs are impressively tough.