The main difference is that the Lanes live outside of the host track, like automation lanes do. Layers, on the other hand, would all live in the main track, and things could get very small and fidgety if you had a lot of takes/ layers in a single track.
There's also a section for writing notes next to each lane, as well as per-lane Record buttons and Edit Filters. As such you will be able to record directly into a given lane and also show Clips or AudioSnap transients on a per-lane basis, all of which were impossible with layers.
Additionally, the Inline PRV behaves uniquely as its own, independent PRV in lanes on MIDI and Instrument tracks. So, you could have multiple Lanes on a single track driving different parts of a multi-timbrel synth (handy for MIDI drum arrangement and other things). Or be able to manage different MIDI takes in their own, separate Inline PRV for editing, all with their own Mute, Solo, and Record buttons.
As you can see its a pretty big feature that touches many aspects of the program. We should have a blog post about this feature in the coming weeks with screenshots and a more in depth explanation.
SP