Hey gunspike,
If you are asking to apply to X curve Bezier keys and to Y linear, currently it's not possible. It will be added in the future.
From your example I can see that you are making a ball jumping on the same spot, so your Y curve has changing values but your X has only one value, meaning, there is no movement in the X axis. It means you don't need to touch this curve at all. When we will have keying X and Y separately, you could delete all the keys on the X-axis (except the first one).
Check out our graph video https://www.youtube.com/watch?v=37CeFRzrjqc&t=29s. I animated a ball bouncing through space at the beginning of the video. Here the workflow is really important. First I planed the timing, then I made Ease In (or Slow In) to the last key on the X axis, then I added the keys for the Y axis bounces, and for the end, I added the rotation of the ball. Try to replicate it!
Hope this helps.
@foriero re: easing, every time you put the Bezier keys you get ease out/in between two keys. And the power of the Graph is to then customize your curves to get really good animation.
