If Apple were to release low level documentation and source code for hardware it considers obsolete to help developers support it, it would not effect their business other than getting a lot of goodwill.
it may not affect them at a pennies-in-billions level, but those pennies are owned by a few patent holders whose heirs will profit many times over in the foreseeable future
why? I doubt those obsolete chipsets will be used by anyone else, or anyone will be particularly motivated to shell out a lot of money for access to schematics.