> It would make some sense as mis-managing the fuel-air mixture on a small piston plane can lead to catastrophic failure. (frozen carb for ex)

Carb freezing doesn't occur as a result of mixture mismanagement, but rather by failure to apply carburetor heat when flying in conditions conducive to carb icing.

Mismanaging the mixture is far less likely to have any acute effects. Descending with a lean[er] mixture may cause issues at lower altitudes where the mixture would be too lean, but it would be unusual for that to lead to an engine stoppage.

Further - a pilot inexperienced in mixture management would likely not lean the mixture at all and just fly full-rich which again, wouldn't likely lead to any acute failures, just higher fuel consumption and longer-term issues with the engine.

I can see a series of errors causing issues; eg. flying rich long enough that any buffer fuel in the tanks is exhausted prematurely.

Unfortunately that is a fairly common cause of fuel exhaustion incidents.

It makes sense to me that moving from electric to piston would require an endorsement. Asking for a rating seems like overkill.

> It makes sense to me that moving from electric to piston would require an endorsement.

For a long time, it will be the reverse; the default will be a requirement to be able to fly a conventional-engined airplane, with electric propulsion being an endorsement (probably devoted primarily to battery & power management)

Perhaps either way should require an endorsement. Gasoline is hard to fly... tank switching, carb heat, warm-up requirements, power output limitations, mixture at takeoff, mixture at altitude, thermal management in power reduction, weight of fuel in load calculations. In some models even CG due to fuel load. The list goes on and on. Electric ought to be much simpler to fly.

Flying gasoline-engined airplanes is already the default. I suspect it will stay that way until the numbers shift noticeably