Starting from Update 2.00 we have been taking the opportunity to list some of the modding-related changes which normally go unannounced into patches.
X4 Wiki - Breaking Changes
Please note that this will always be just a subset of the changes which may have an impact on mods, but at least it provides a little more information to modders. Added features such as new script actions or Lua/FFI functions are not announced, since they will not break existing mods. However, the corresponding documentation will be updated (e.g. XML schemas in the catalog files).