The particular forward compatibility issue is related to a one-time padding change in the AssetBundle header which has been backported to the version in question. Typically such changes that break forward compatibility should be very rare because the AssetBundle format is quite stable and well established. In general we also do not support forward compatibility of AssetBundles because the serialization and heirarchy of objects in a bundle may change in a way that older versions of the code cannot handle (the same is true for scenes and other assets)
However although we cannot fix the specific case mentioned, we have opened up two follow up internal tickets, e.g. to make sure the hash incorporates the unity version and to expose the unity version in the .manifest file.