I’m alternating between two chains on a 9-spd Shimano Steps bike. I’m up to 3100 miles and no issues yet. Have no idea of wear, but it rides fine. One chain is KMC, the other the original Shimano. 250W stock motor. 25kmh cutoff.
I think mileage depends a lot on how much the motor has to add.
My average speed during urban riding on a regular bike is pretty much the same as the cutoff speed. I use the lowest assist setting. The motor isn’t making me any faster, it merely takes the edge off starts and climbs.
So I’m thinking, if I can hit the same average w/o the motor, then the motor can’t be working the chain that much harder, and I should get a fairly similar chain life.
A friend of mine bought an ebike for his wife, which increased her average speed by 1/3. And halved her maintenance intervals.