Also would ask an open question: Would it make sense to consider the possible exposure of the Concurrency hooks and backtrace information together (I read "ability to programmatically capture a backtrace" as basically a 'live sample' of the application to introspect current execution state - the related link had a similar request to introspect current state for Tasks etc, perhaps there is some possible synergy in the design space for how to expose it (Runtime Introspection ?, just food for thought).
FWIW we had great use of our external tool for capturing stack traces in a previous life