He probably means that it should start consuming bob's resources for the higher tiers (Similar to the bob version of solars) and the higher you go, the more complicated it gets. I.e. Steel for MK1, Titanium for MK2, Tungsten for MK5 etc.
Obviously it's completely up to you how you want to set it up for bobs (Perhaps you even want to add small and large versions of these MK versions like bobs?)
i.e. it just depends how much you feel the time investment is worth it to program compatibility, balance and whether or not you even feel it's worth it.