You don't really need house rules to deal with a mage with cyberlimbs. He will already suffer Essence loss (and Magic loss) from it. Cyberlimbs give you a boost right out of the starting gate, and let you be potentially good in combat even if Agility and Strength are your dumpstats, but on the other hand, cyberlimb Attributes don't affect your physical limit, and over the long term, someone with muscle augmentation/toner and/or bone density augmentation will be better overall.