Humans are given the free, totally optional choice of converting into Cybermen. Completely self sufficient walking suits of armour, no longer needing food or sleep, just electricity. Superhuman physical ability and eternal life, but with emotional inhibitors. Not exactly an attractive option for anybody who enjoys being human.
Thing is, it's a pretty much guaranteed chance to survive the inevitable over-heating of the planet and the dwindling of its natural resources.
How many humans do you think actually go for it
The basic premise is sound. Being an immortal being of pure intellect is a pretty good deal in general, and one I would 100% take.
However being a cyberman would be horrible.
Not just cause of the emotional inhibitor, but because of the whole mind controlled into turning other people into cyberman and being so massively traumatized that if your emotions ever turn on again you commit suicide basically right away.
Not sure how many people would actually do it. There are a ton of desperate people out there, and I could see a good portion of really old people who know death is right around the corner and in an immense amount of pain going for it. Sure, you would never feel the touch of a lover or the feeling of sunlight on your face ever again, but that's already the reality for a good chunk of folks.