1: perhaps more perfect analogy will be socketing ROM as its own chiplet if that ever made sense
Not that it was an official licensed product, but for what it's worth, there was a DS flashcart that bundled a significantly faster CPU than the DS's own - the SuperCard DSTWO [1]. The extra CPU (Ingenic Jz4740, MIPS) was primarily used for GBA emulation on DS/DSi systems without the need for a GBA slot passthrough flashcart, as was otherwise required - though there was a quite successful homebrew scene around it at the time as well, up to and including stuff like a (proof of concept) port of a PS1 emulator [2].
It was a surprisingly impressive device! The only downsides, as I recall, were the increased battery drain and the fact that the DS Slot-1 bus was only fast enough to allow streaming video output from the cartridge to the system's displays at ~45FPS, irrespective of the rate that the emulator was actually running at internally.
[1] https://wiki.gbatemp.net/wiki/SuperCard_DSTWO [2] https://gbatemp.net/threads/how-to-play-ps1-games-on-your-ds...
It's called the Didget blood glucose monitoring system, and I found it here: https://en.wikipedia.org/wiki/List_of_Nintendo_DS_accessorie...
https://en.m.wikipedia.org/wiki/Guitar_Hero:_On_Tour#Gamepla...
Edit: a better picture of it in action, https://en.m.wikipedia.org/wiki/File:Guitar-hero-on-tour-ds-...
