Well, I am trying to build reusable components to manipulate parent actors in UE4… 
That’s what they intended for, aren’t they? As blueprints itself still aren’t composable, that’s pretty much only way without C++, I fear. I really can’t see reason why asynchronous operations like timelines shouldn’t work in principle, at least for actor-, or scene Blueprint scripts.
Sounds more like an internal problem with architecture of engine to me. I don’t have necessary background knowledge but I really don’t think this restriction is only a matter of logic?