These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Long Earth
Call Back: Possibly. Mary the Troll's "I will not" response to researchers asking her to give up her baby to be used as a test pilot in The Long War - which becomes something of an in-universe Memetic Mutation - echoes the golem Dorfl's rejection of an order to kill a human ("Not Thou Shalt Not, Say I Will Not") in one of Pratchett's earlier Discworld novels, Feet of Clay. Also, Joshua's attempt to escape from the Beagles on the river resembles Vimes' plan to avoid the werewolves in The Game from The Fifth Elephant.
Expy: Possibly. Fan speculation has linked Lobsang to the character of the same name from Thief of Time, somewhat justifiably since the Lobsang of Discworld is an anthropomorphic personification of time itself, and therefore presumably could be reincarnated as a human/sentient-robot/hybrid on Roundworld if he took it into his head to do so. However, the character of Lobsang in The Long Earth has more in common in terms of personality with the Discworld Lobsang's mentor, Lu-Tze, than the character himself.
If it turns out there's any truth to this theory, it will also count as Canon Welding for Terry Pratchett.