The Time Lords are really one of the few alien races the Doctor can be genuinely intellectually intimidated by; that's why I'd like to see them back again. Most races are basically either children or curiosities to him, with the possible exception of the Daleks and maybe one or two others. He may care for many of them, but there's always a power imbalance in the relationship. Time Lords, whether adversaries or allies, have to be taken more seriously by him.
Not just someone to teach, impress, protect, awe or defeat, but a person to talk
to in a way only adult equals can. That's the dynamic I'd like to see if the Time Lords ever returned. The whole power/corruption/"jerks" angle discussed upthread is a mirror I'd love to see the Doctor be forced to emotionally & intellectually hold up to himself in a meaningful & literate way.