The cyber is an entire biome made out of machinery, it just doesn't go with the Hallow. An alternative biome should share a link or theme with the original while still being unique. The crimson did it perfectly. The Covert honestly would too, and so would the Glade.I agree that the developers' resolution for the game isn't to make everything follow the same unchanging template, but saying that the cyber doesn't fit Terraria for that reason is just untrue, we have invasions which all include advanced unorganic technology, like seriously there is a plant that drops a modern gun, I don't think it's fair rejecting the cyber for that reason.
The cyber doesn't share any resemblance to the Hallow, at all. Making it directly to be the counterpart for the crimson and to only spawn in crimson worlds is not very terraria like. Considering the fact that when the devs added the crimson they still let the hallow spawn in those worlds, we already know they won't go down that path.
My argument for the natural organic theme major applies to biome, but small to other things, as biomes are vastly more significant and that is why we want more alternatives.
I would kill for a hallow alternative. I would also be fine with another world evil. However, ultimately, the cyber wouldn't function as either.
Edit: The martian invasion is still organic because life is controlling many of the machinery