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In the Apple IIgs computer, the address and data buses of the 65C816 CPU connect directly to the onboard ROM, except for A14, which, according to the schematic, is routed through the FPI ASIC. There's no mention of this or why in the Apple IIgs Hardware Reference.
What function does the FPI chip perform on the A14 signal? Does it merely buffer it, or is the behavior more complex?
I might be wrong, but AFAIR it was something already present on the Apple IIc to support a 32 KiB ROM image instead of a 16 KiB (starting with ROM Version 0). For ROM access either half could be selected. So this isn't really A14, but the ROMs A14 to select one of two 16 KiB regions.
