Messing with 18650s is rather risky, I'm not sure if exposing them as individual cells is a good idea. I hope the company is smart enough to put a "if you burn your house down replacing the batteries, we're only liable if we sent you the replacement" clause in their sales contract or they'll be sued into the ground if this thing ever takes off.
As for ARM+games: with tools like Box64 you can get some impressive performance out of 3D games assuming your GPU is supported. The native code of the game will be running translated, but the expensive calls to 3D engines and such will all be caught and replaced by native ARM libraries. I doubt you'll be running Cyberpunk on this thing, but don't count it out just because of the translation step.