I know it's still beta and probably a lot of work left to do on the Timeline, so I can just comment on the current state.
Coming from a background in with a lot of motion graphics work, using software like AfterEffects, Maya, the timeline feature seems at his quite a long way to go to be a great timeline. It currently works but there is a lot to wish for.
I tried it briefly yesterday, and apart from being very buggy, it lacks some of the most important features to be a useful animation tool. I will highlight some things I found very strange and hopefully not working as intended.
Scrubbing is a pretty crucial part of animating things with a timeline. You need to be able to put the current time indicator (the red line) at a certain point and immediately get feedback to where the object would be at that current time position. You need to be able to click-drag to scrub the timeline back and forth to get a feeling of your animation, without having to press play every time.
At this point you can only choose various tween options between points, but in the future I hope it's planned to have a curve editor to manually edit curves. If there's no plan for it, at least the timeline could use a good visual representation of the type of tween between the points.
I don't know if it's a bug, but previewing the animations in the layout object just jumped from one keyframe to the next, without any tween being previewed.
Auto Keyframing or Record Keyframes
Very useful for quick animations. It works like this: If the timeline is at position 0s, you then move the marker to 1s, and move the object a bit, to where to object is supposed to be at 1s, it will automatically place a keyframe there with the correct value. I don't know if there's a hotkey for add keyframe. Whenever I added a keyframe, I had to go to properties to set a value for that keyframe. Not very user friendly.
Useful Keyboard shortcuts: (maybe they exist, but I havn't seen any documentation of what those are yet)
Set keyframe: example (s, or k) or something like that.
Play all timelines, (space or something similar)
Quick add all translations
When adding an object to timeline, it's good if you get an option to add all properties. X, Y, Rotation, Width, Height, opacity, in the timeline easily. This makes a lot of sense, if you already know you will be animating many properties of that object. This will work well with the Auto key function, when you have an object to animate, and if you edit any property of that object it will automatically make a keyframe, at current timeline position.
Those were just some if the things I noticed on my quick tryout.
Edit: Properties I was missing as well, was to set animation and animation frame. That's something i would like to control with the timeline as well. Maybe you can do it as a workaround by using instance variables, then setting animations, and animation frames to that variable.