Except (1) Switch 2 game servers will not likely go down for at least 2-3 more decades. You can still redownload Wii games purchased, even though the Wii eShop closed down in 2019; which means that the store has already been available for past purchases for 20 years already. (2) Some of your old disc-based games are already kind of just a piece of plastic. I have 3DO and Sega Saturn games that have developed disc rot despite carefully looking after them, and in many cases your old video games console is no longer working. My Game Gear is no longer working because caps blew and leaked - a very common problem with some Sega systems, especially the Game Gear. My Amiga 600 floppy disks are also no longer working - they have long been demagnetised, with expected life spans of 5 to 35 years, I can no longer play Return to Atlantis or Lotus Turbo Challenge 2. I also have Tornado on DOS CD-ROM which also suffers from disc rot.

The only meaningful and realistic and guaranteed game conservation method is to rip your games onto an ISO/ROM and maintain them this way via emulation or via a flash cart. 

Game key cards solve for me one key problem of digital content: Transferability. Not being able to sell any of my hundreds of Steam games - this is a much more real problem for me than having to worry about whether or not my copy of Panzer Dragoon Saga will still work as-is on my Sega Saturn in 2040.

Whole-heartedly agree with this. In fact, that IMO highlights the main issue with GKCs— when the game isn’t fully on cart, you can’t just simply rip the ISO/ROM file via the cart.

Granted, if people informed on how to rip/emulator games come up with a way to rip the files directly from the system without a need for the cart (as they undoubtedly will), then preservationists have nothing to worry about. BUT if that never comes into fruition, especially with have aggressive Nintendo has been against emulation as of late, then yeah, that’s a big problem.

I understand the issue with GKC, though that doesn’t change that I still view it as a tad bit hysterical for the exact reasons you lay out Helloplite: Nobody truly owns the software for their plug-in-and-play consoles.

Roughly 3% of discs will rot once a decade according to a study by the Library of Congress. This is of course if you store them at 70F and 50% humidity. So after 100 years 70% of discs will still work. 

There's a new PCB board for many Sega systems including CD and Gamegear. Honestly, unless a chip is completely dead any system can be repaired. Lasers are recappable and serviceable. Motors, gears, shells, pins, caps, and lasers all have new replacements. 

P.S. Leynos insulted you because you are the 100th person to come in here with "nothing is on disc anymore" nonsense that I have debunked repeatedly.