honestly, the thought had crossed my mind... like the shot of him in the basement of the senate building... talking to Anakin in Episode III... but I didn't want to add that in... it would be up to Ady.
I personally liked the dynamic... if you really study the scene, it makes perfect sense.
Vader already knows about Luke. The emperor calls to pretty much say it's not safe, that Luke exists... trying to drop a bomb on Vader who kinda already knows. He tries to downplay Lukes importance (while at the same time, trying to hunt him down himself).
He's also calling to say that Luke cannot become a Jedi... which I guess insinuated that Vader should destroy him before he destroys them...
But his emotions get in the way and he suggests that if Luke can be turned... trying to find a way to not have to kill him... to keep him....
Now... mind you... Vader is kinda showing his hand here... How many Sith can there be? ...2 right? If he wants to turn Luke... he's in essence saying "I want to replace you." ... although I'm not Certain that Vader realizes it when he says that. Calling him an Ally... maybe meaning not a full fledged sith...
He has tried it before... in Episode III he tried to convince Padme to rule with him... look where that got him lol.
I think the hope was somewhat the same here.
BUT Palpatine, realizing that, thinks "I'll play along... but instead of replacing me, Luke will replace YOU at my side... " as we latter see him try in Jedi...
And it would go a long way to show the crumbling relationship in ROTJ... how Palpatine doesn't even want to see Vader... he's to obsessed with getting Luke he doesn't care about Vader anymore.
I think its kidna cool at least lol