FAI and AMA Fast are two different events. A LOT different.
For starters, Fasts have .36 engines, vs .15's. Over twice the power and danger.
Furthermore, AMA rules END the match in the event of kills, crashes, collisions, line tangles, and flyaways. In FAI, the show goes on, pretty much, no matter what. Thus, in FAI you need to have a shutoff that can survive an "incident" and not put you out of action.
If it takes you 3 models to win an AMA Fast contest, it might take a dozen to win a similar-size F2D meet. That's a slew of shutoffs.
In AMA Fast combat, the flyers failed to do anything when Nelson engines put airspeed through the roof. They clung to .018" lines (which were mandated due to the SuperTigre C35). In a way the shutoff rule served 'em right.
F2d is another story. Since it's acceptance in 1976, there have been several speed-reducing actions: upgrade to .015" lines, 10% nitro, 4 mm venturis, and mufflers. Airspeed remains at about 100 MPH, far below it's peak of 120 before the rules changes. At this time there is no emerging problem that would logically justify shutoffs. It's a simple case of Monkey See / Monkey Do. AMA put in shutoffs, so FAI followed suit.
I don't expect this to kill the event, but it will be substantilly downsized, unless a miracle fix emerges from the Ukraine. Maybe some cheap, clean, domestic gas for our cars, too.