If we wanted to remove the line, I imagine it’d be best to simply remove the footage where it takes place. Maintain the pace, just without that line present.
I agree with Hal. If the line is going to removed, the scene will have to be tightened up around it in order to avoid a lot of dead space.
As for whether or not to… I go back and forth. On one hand, it’s just about the only time the movie even tries to connect TROS with the rest of the trilogy. On the other, did we (the audience) ever hear Vader speak to Kylo in the other films?
In TFA, when Kylo is speaking with Vader’s helmet, I kind of like the idea that he’s begging Vader for guidance, but he hears nothing in return; because Vader became Anakin again, and Kylo doesn’t realize that “Vader” is gone. That was always my read of the scene; and I suppose, thinking about it, Palpy’s “I’ve been pretending to be your Evil Grandfather! Bwa ha ha!” line does undo a lot of that nuance.
EDIT: If we decide to gut that line, it would probably just be easier to cut the Snoke part too, and just say “My boy…the First Order is just the beginning.” As Jarbear said, Snoke seemed to be operating independently of Palpy; and at this point, Snoke doesn’t even matter to the story. He’s already been removed from the Clone Vat (thank God for that, by the way). Maybe it would be stronger/more logically consistent to just have Palpy stand apart from Snoke entirely? Sort of take over where Snoke failed?