Is this our relationship now?
Further evidence for my theory about Moist being next Patrician: in Raising Steam Vetinari mentions Leonard of Quirm to Moist in a way that makes it clear that he has him nearby, and Moist later has an internal monologue that speaks about him as though he knows him personally. There is absolutely no way Vetinari would have let Moist in on the Leonard of Quirm secret unless he wanted to make sure he'd be taken care of when Vetinari wasn't around later (because Leonard is useful to the Patriciancy, and I doubt Vetinari would take him with him wherever he was going, no matter how fond of him he is).