We already have this:



But now we also have this:



That's a bit confusing... why is APEX's channel list just the old channel list, but APEX's animation layer is a totally new thing?

It's very likely that the old animation layers pane will be hidden/removed. The difference is the the old animation layers pane worked with parameters with nodes anywhere in your Houdini scene. The APEX Animation Layers pane only works when you're trying to animate on a particular APEX Animate SOP and will differ depending on which one you have active.