I've been thinking about this a lot these last months, as I wanted not only to be able to change the parent of a layer, but I also wanted to be able to do it with a precentage... I did it!
This means you can parent a layer to several other layers at the same time, you can animate the parenting, and animate it smoothly - not with a checkbox!
- Rigging > Links and Constraints > Parent Link
- Click on the button with a layer selected
- Adjust the parenting in the effects of the layer
- To have multiple parents, duplicate the effect.