If they want to bring back the Time Lords, here is how they could do it. Explain that a handful of Time Lords escaped just before the end. They went back in time and using genetic engineering, over time, cloned an entire new civilization of Time Lords that have been hiding from the universe all this time. After growing in strength, they decide it is time to reassert themselves as the master civilization in the universe. Since they are clones, the show could portray some similarities with the Time Lords from the old Who while introducing some new elements as well. They would not have to behave exactly like the Time Lords of old.