If you wonder what happens if you go pretty far away, you're welcome.
Since we're using computers, I'll write what happens every power of 2.
I'll go along X axis, leaving Y axis at 64. Keep in mind that if you go along Y axis same happens as well.
2^6 (64): Pretty normal, huh.
2^18 (262 144): The game is still playable, but you can notice that OpenGL is giving up since it's giving black stripes of nothingness. You can interact with the environment.
Inbetween 2^18 and 2^19 (393 216): Physics engine is giving up as well. Every object physics is distorted, but you can still can interact with environment.
2^19 (524 288): Something incredible happens. Right after 524 287, you meet an invisible wall. From 2^19 and to infinity, you can't move along that axis, but the remaining one is still "functional". You can interact with the environment.
P.S. Huh, could this ruin rocketry? I don't think so.
2^20: Physics engine is suffering. Just look at the cat! The physics for it is amazingly distorted! OpenGL giving up even more. The black stripes of nothingness intensify. You can interact with the environment.
2^22: Now I definetely can say that physics engine suffers even more. No, physics not just distorted, but it also came out of existence for the small objects. From this point, it's hard to interact with anything.
2^23: Physics distorted even more, and "interaction hitbox" is distorted as well. Try to interact with anything, because you probably can't!
2^24-126: As I'd like to call it, the Edge of the World. It really is: if you go further than this point, your camera won't move, but cat will.
2^24-124:
2^24-122:
2^24-120: Cat disappears in the void.
2^24-116: Left half of the camera goes in the abyss as well.
2^24-114: And also the right half.
2^31 - the 32-bit signed integer limit: game lags so much your patience probably couldn't handle it.
From this point, you're unable to move further away with movePlayer command.
That's it. These are all the limits of MewnBase.