I've recently tried to write a cmdlet that had to use async APIs. Doing so turned out to be incredibly difficult, and with help I found an AsyncCmdlet class that lets you override processRecordAsync etc. as async functions that get CancellationTokens:
https://github.com/felixfbecker/PSKubectl/blob/master/src/AsyncCmdlet.cs
https://github.com/felixfbecker/PSKubectl/blob/master/src/ThreadAffinitiveSynchronizationContext.cs

Could PowerShell provide this out of the box?