The limitation in question is for a pool of Variable Abilities similar to Modular Abilities, i.e. mostly physical abilities such as Strength/Speed/Toughness etc. Now, instead of changing the abilities on the fly, the character has to prepare artificial bodies custom tailored to the specific powerset, and to switch powers the character has to switch to a body that has the desired powerset. Creating bodies is something that takes a certain amount of time (~1 day per body, not sure on that part yet), and the total number of bodies would be limited by something such as workshop rating. Only the currently inhabited body is sentient, while all the others are inactive. Think of it as an AI jumping between various custom tailored robots.
Now, what kind of Limitation rebate is fair such a restriction? The modular pool in question would be in the (low, starting with 1X) double digits, if that makes a difference.