Definitely. Cartridges really were amazing; I think that's ultimately going to end up being the organic thesis of my web site.

Something I discovered while researching this post: Sega had their own Super FX-y thing with the Sega Virtua Processor. It was only used in one game (https://en.wikipedia.org/wiki/Virtua_Racing), but the thing I find most fascinating about it is that Sega contemplated releasing just the Virtua Processor itself—you guessed it, as a lock-on cartridge.

(Unfortunately, this fact didn't really fit in anywhere, so I'm just dropping it here.)