If a majority of miners implements new rules that the validating nodes don't support, then the blocks are just ignored. They may as well be mining Bitcoin Cash

If a majority of miners implements new rules that the validating nodes don't support, then the blocks are just ignored. They may as well be mining Bitcoin Cash or Litecoin blocks. The majority of miners implementing new rules only has an effect on which rules the validating nodes will start enforcing if those nodes implemented them and allowed miners to signal when to start.