Families should be a good workaround for this. There are two reasons why there isn't a generic system action for picking by UID which does not specify an object type:
1) suppose it exists, and you use the condition. Which object do you put the action under? You don't actually have a way to use the object you just picked.
2) there are some pretty complicated optimisations in the event engine to ensure picking happens fast when it comes to subevents. One of the things it needs to know in order to optimise this well is which objects might have their picked objects changed. A condition which could pick from *any* object type therefore means no optimisation can happen. Due to how the engine works, running that event would take O(n) time, where n is the number of object types in the project. So the bigger your project gets, the slower that condition would get. It is more important to make bigger projects fast than smaller ones, so that's not acceptable.