It would be very handy to be able to click and drag for both dimensions of multidimensionnal properties (or spatial properties only?) in the timeline (like positions), using both axis of the mouse.
This could be done through an additionnal icon, to keep the current behaviour on individual axis (see screenshot example)
In case the property has three dimensions, this icon could be used to adjust only X and Y.
This would make it easier to work with layers while hiding layer handles, allowing us to quickly move the layers without selecting/clicking in the viewport.
Working with hidden layer handles improves a lot the interactive performance, which is very important when manipulating layers/rigged characters for example. It is also a big comfort as you can see the actual image you're working on, not polluted with handles.
Even with handles, being able to move the layers like this is a good way to avoid inadvertently scaling the layers with the handles in the viewport, something we do so often people add expressions in the scale properties just to 'lock' them 😉