rF2, AMS and ACC really deserve dynamic gearbox and drive-train flex simulation imo. It's something that many people may not even be aware is missing but, the more you pay attention to details, the more a lack of such physics modeling becomes a missing link in the system. Update: ACC now has some drive-train effects working (since v0.6); not quite enough flex yet imo but, getting there.
For those with a good motion system, the titles that have effective elastic-modeling (iRacing and RaceRoom), truly stand out because the effects can be felt so directly and physically. The more powerful (and vintage) cars take on a whole new character and provide a much more immersive experience when the connection to the virtual car is enhanced with the proper physical modeling but, even track-day or novice-class cars can benefit.
iRacing is far ahead of the pack in this regard, as their model seems to be quite advanced judging by the subtle ways that it interacts with both the engine-load behavior related to tire-surface contact (bumps, curbs, short-term traction-loss) and even, over-fueling & electronic-assist conditions (engine stumbles, rev-limiter, rich fuel, etc.).
I'm a bit surprised that these effects get so little attention, especially when many sim-racers want more realism in physical behavior in general. Drive-train elasticity is one of the most fundamental aspects in race-car behavior as it relates to the mechanical interaction between the power and drive-trains.