But to go the route of more justification ("know their true lineage they cannot...") or to just avoid the issue until Vader reveals it to Luke has to be considered a back-up plan until it's proven that this cannot work -- at least in my opinion. The reasons are clear to me:
The "reveal" in ESB is broken in the Saga. We already know the truth. The only reason it worked in the OT as a "reveal" is that we didn't know. Not even Lucas knew.
The "reveal" had problems even as it was played in the OT -- not only did it make Ben a liar in ANH, but as he and Yoda train Luke and then watch him leave for Bespin -- why don't they tell him? He's their only hope (Leia ain't gonna take over where Luke left off). If they told him on Degobah, Luke may have stayed -- he would definitely be better prepared for the eventual revelation. But they don't tell him because it would screw up the "reveal."
Then ROTJ is all about Luke's sudden awakening to the good inside Vader. A "good" which was nowhere in evidence in any of the first two movies. But, by golly, Luke was right as Vader starts mooning around about his inner conflict.
This is the SPINE of the OT -- and it's fine and pleasant as they played out originally. They were astonishing and fantastic. But they barely hold together -- and with the introduction of the PT, they creak very loudly.
But IF (and I admit it's still a big IF) we can get Ben to be honorable. Get Luke to know his parentage. Make Yoda's training clearly about facing Vader. Make Luke's rash decision more informed. Vader's surprise will be less SHOCKING, but the same decision by Luke remains: he chooses to destroy himself instead of join Vader. But now that scene actually reflects some insight into Vader -- Luke knows Anakin is still inside there somewhere because Vader reaches out to him when we thought that side of Vader was dead.
Then ROTJ will have the power its supposed to. Then it really will feel like the CLIMAX of the Saga instead of the limping collapse of the Saga which is more how it feels to me now.
It'll be concrete ideas that sway anyone's opinion, I know. One thing I learned on the SOTD thread is that Trooperman's clear vision and dedication to crazy ideas (over-dubbing Anakin!?!?) won me over in the long run. I'm at the "drawing board" still with this "Ben Tells the Truth" version of the OT -- but I deeply believe it will improve the entire Saga.