Has anyone tried putting the Powered Up system in the Christmas train?
Haven't done the 10254 yet with powered up, but have converted several other trains... The train motors have the exact same dimensions and the powered-up smart hub has the same dimensions as the battery box of the power functions system.
What's different is that you don't need the space for the IR receiver and that the motor is immediately connected to the hub rather than the receiver.

What will differ is the following steps from the instruction manual:

Those steps make room for the IR-receiver which isn't necessary now..., for the rest you can follow the instructions exactly...