As far as I'm aware, ACR/Lr will continue to deal with reading image settings (e.g., in XMP sidecars, embedded XMP metadata, etc.) in the same way as they have for several years: Namely, they will be able to correctly read settings from current and earlier versions, but may not be able to read settings from later versions.
Example: ACR 8.1 can read image settings created from ACR 8.1 and earlier (ACR 8.0, ACR 7.4, ACR 4.5, ACR 3.7, etc.) but not necessarily later versions like 8.2.
For instance, ACR 8.2 introduces a new Color Smoothness slider and a Feather control for spot adjustments. If you use these controls in ACR 8.2 to edit an image and save your settings (click Done in ACR), the settings will be written into XMP metadata. However, if you then try to process the same image in an older ACR version (8.1, 4.5, 2.4, etc.) they won't read those new Spot Feather and Color Smoothness settings correctly, obviously, because those older versions don't support the new controls.