Both good choices. Pete Doctor has been solid for a long time at Pixar and Jennifer Lee, aside from Frozen, Wreck it Ralph, etc, also wrote the story for Zootopia.
Aside from the reason for Lasseter's departure, I think it was getting to the point of it being time anyway. Pixar has been in a bit of a weird place since about 2010 with a mix of hits and misses. WDAS, which Lasseter had less involvement with, has been thriving of late.