The Famicom didn't even have the connector. It had a standard off-the-shelf 15-pin connector instead, which was mainly used for external controllers. The Disk System instead connected to the Famicom via a RAM adapter that plugged into the cartridge slot. The NES expansion connector was intended to be used for a localized version of the Disk System, but as you mention this was scrapped in favor of cartridge mappers. After this, Nintendo then planned to use the expansion connector for a localized and expanded version of the Famicom Network System modem (see https://archive.org/details/0966961706/page/390/mode/2up ) but this also ended up getting scrapped.