Plenty of old consoles had strange unused features. For example, the Megadrive VDP outputs the palette indices for each pixel in addition to the analog RGB output. This feature was used by the System C board (a Megadrive in an arcade form factor) to attach an external RAMDAC with higher color depth and more on-screen colours, and has been used recently to provide native HDMI output (https://www.megaswitchhd.com/).