Flygen AWES require light generators aloft that rotate at fairly high rpm. However, as an example (see page 44/51), life expectancy of the EMRAX motor is the same as life expectancy of the bearings that are mounted in the motor. And for longevity, low speed (1800 RPM) is superior to high speed (3600 RPM).
Magnetic bearings have a higher lifetime and are used for gas microturbine generator type which rotates at very high rpm while its lifetime is high, being about 50 000 - 80 000 hrs, the higher value shown on this table.
And to see more: micro generator for gas turbine , High Speed Generator for Gas Microturbine Installations , Development of a high-speed turbo-generator supported by active magnetic bearings, describe generators with rpm in the tens of thousands.
So there are some possibilities for both lightweight (about 5 kW/kg) and durable generators.