Alas, sometimes it just is not possible to maintain backward compatibility, especially if a script is directly reading files like mirc.ini, servers.ini, and so on.
There are times when a change has to be made to the format, eg. if a feature is being extended/updated/fixed, and there is no easy/non-convoluted way to make sure that scripts, or even older versions of mIRC, will be compatible with the change.
In this case, there were requests that the favorites be moved out of mirc.ini, and as much as I did not want to do that, I think it makes sense in the long run.
As for redirecting $ini(), $readini(), /writeini, and any other related commands/identifiers that a script might use to access mirc.ini - that is not something I would want to do. It would make the script think that a section exists in mirc.ini when it does not, with all of the subsequent issues that could lead to.