Yes, it’s the adjective form of -mancy, so cytomancy would be cell/cellular magic, and a cytomantic slug is a slug with a cellular magic property of some kind. Think of necromancy/necromantic.

By etymology that would mean cellular magic, make of that what you will

I read it more like the new, better standard is never developed because someone used the real xkcd as an argument against making the new standard

It should factually reduce the cost of building housing as that is one less thing to build. How much that cost reduction is going to translate to lower buying/letting prices is a different question, I agree

That sounds like a welcome reduction in housing cost in an expensive, densely populated city with good public transportation