For what it's worth, the semantics you're asking for may be actually expressible using the new APIs we're adding right now: "immediate tasks", please check the review thread over here: [Returned for revision] SE-0472: Starting tasks synchronously from caller context - #3 by ktoso
Basically, this introduces group.addImmediateTask {} which very aggressively start the task on the calling context, regardless of any closing over it or not. The existance of that isolated parameter in the surrounding context will be enough to achieve this.