Parent Layers in Time
The ability to have layers dynamically connect and interact with each other in the layers panel would tremendously increase productivity and save artists clicks. Specifically, the ability to lock layers in time with each other, parent layer in and out points. This would work really well in situations where you need to split a layer to get one part of it on top of the stack, but when you need to adjust it's in/out points afterward, you don't need to do it for each split that you've created.
A video example can be found here: https://vimeo.com/136890745
Bran Dougherty-Johnson commented
Great idea. This would save people tons of time when they need to change an edit to match new VO or other revisions that would end up shifting lots of layers in and out points and currently have to be done manually (and very carefully).