I think the Game Boy Advance was the last mainstream PCB cartridge game console. The GameCube had moved to discs, Sony and Microsoft never made a cartridge based system, and Sega was on their third such system with the Dreamcast.
But I don't think the GBA or N64 really did things like the SNES or NES did with regards to cartridge hardware. I think by that time, the core hardware was way more powerful than anything that could be attached.
I know hardware homogeneity across platforms brought peace upon gamedevs who are stressed out as-is, but I think we lost something major along the way.
Some games even got multiple releases with different save chips. Metroid Fusion originally released with static RAM and a battery, but later cartridges feature ferroelectric RAM and no battery. As far as the software is concerned, these two function the same.
My favorite is WarioWare: Twisted [1] including a gyro sensor (+ a rumble pack) to enable gameplay based on turning the whole GBA around. But there were also add-on real time clocks (Pokemon), light sensors, and other things.
It also had the Nintendo e-Reader [2], which technically connected to the cartridge port and loaded like a cartridge, but was its own unique piece of weirdness.
GBA medical device.
Also, a new DS flashcart just came out, from the same makers of the popular EZ-Flash Junior for GB(C) and EZ-Flash Omega for GBA. It's called the Parallel. It costs considerably more than other DS flash carts, but is still cheaper than flashcarts for GBA or anything older (NES, SNES, and N64 flashcarts are insanely expensive).
MachoNachoProductions on YouTube has a video on the Parallel.
I don't know if all the enhancement chips were collected and decoded, as IIRC a pair of them are literally used for a single japanese-only game.
Although for IP reasons the enhancement chip firmwares can't be distributed with higan, so you have to "dump them yourself".
All the enhancement chips used in officially licensed games were collected, decapped, and dumped via an electron microscope. Yes, even the ones only used by a single Shougi game each. :)
I still can't get over the tragedy of what happened to them. That shouldn't have happened under any circumstance.
from https://eu.usatoday.com/story/tech/2021/07/23/how-toxic-onli...
That's hard enough for me to think it's legit, though I'd agree that it's not conclusive.
I'm also close to finishing N64 and maybe halfway there for NES (which I have no illusions on completing ever).