It doesn't look like an RMA would do anything, as the new caps would then just wear out the same way. The "W" key has now also started to wear out. I suppose this is because my fingers are always on the WASD keys when playing Counter-Strike, and it's quite hot where I am right now (on a Greek island); 30C/86F with about 65% humidity. I guess the ink (or whatever is used to engrave the letters on the caps) isn't durable and just dissolves away.
I tried replacing the WASD keys with the red key caps that came with the keyboard, but those have a huge problem: they're bigger and stick out higher then the rest of the keys, making them useless for normal usage.
If all generic Cherry caps are compatible with this keyboard, then I guess that's good enough for me. All I want really is for the key caps not to look worn out with the engraved lettering chipped-away. Something without engraved letters would be best, probably. My main problem will be finding someone who ships this stuff, since in my region (Greece) I can't find a single online shop that sells key caps... They seem to be a niche thing.