There’s no evidence in the story for any of that. I don’t truck with pure speculation based in nothing but the instinct to cure defects in the story.
Well, unless Lucas himself pops in to give us his take, pure speculation and the facts from the films are all we have to work with. (And if he does pop in, he’d tell us Greedo shot first, so even his input is suspect.) 
Luke being so in the open as a decoy, I’ll admit is a pretty big leap of speculation. The Jedi might have fallen into ineffectual bureaucracy, but I don’t think they’d go so far as to sacrifice one child to hide another. That was kind of an off the cuff theory I fired off that probably doesn’t hold up in retrospect.
Palpatine knowing all along, I still think could easily fit the facts we know, especially given what a 4-dimensional chess player he’s portrayed as in the prequels and sequels. It explains quite nicely why Vader never knew of Luke earlier. Is there proof? no, but it fits the facts as far as I can tell.
It doesn’t explain why Obiwan/Yoda didn’t put more effort into hiding Luke better in the first place, of course, as they would have no knowledge that the Emperor would keep Vader from knowing. One might say that Obiwan knew Anakin better than anyone, and knew he’d never come back to Tatooine due to painful memories, but again, we’re speculating.
What you do is accept the defect instead of trying to cure it. In the first movie, it’s clear that Luke and Leia aren’t siblings and Darth Vader isn’t their father. The later movies have a different premise with respect to those characters. Just accept the disparity. Don’t try to cure it, don’t speculate, don’t look for a solution. There is no solution.
That doesn’t make for an interesting discussion.
Star Wars is fiction. If the extant fiction doesn’t explain something, we can create more fiction to do so.
The interesting discussion is to note the differences and the differing implications of the two chapters. Have that conversation. That’s interesting to me.
It’s not interesting at all to me to hear people just pull stuff out of their backsides to try to plaster over the disparities. The disparity itself is interesting. Desperate and weak speculation isn’t, when that speculation requires you to cram the story full of incidents and elements that just aren’t there.
Since the word “canon” comes up in these sorts of contexts, let’s look at canon–the four books of the Gospel–Matthew, Mark, Luke, and John. They’re inconsistent. They’re irreconcilable. Yet they’re all canon. Accept the disparity. The disparity is interesting. The conflicts are fascinating. Why do the differences exist? What might have been in the mind of the author of the first part as opposed to the second part?
In this case, George Lucas is the author of both, but we can view it as a person in different stages of life, with different outlooks about the work he is creating.
That’s not a remotely interesting conversation. That’s not even a conversation, that’s the Goofs page on IMDB. I mean, if you’re really keen on the idea, I guess you could start your own thread and hope people are willing to follow your preconditions for the discussion, but I don’t think you’ll get a ton of traction. I think people are, generally, more interested in the sort of conversation that was happening in this thread before you showed up to tell everyone that they’re doing it wrong.
…is literally the least interesting question you can ask about any work of art.
I completely disagree. It might not be the most interesting question, but it’s definitely an interesting question. Look, for example, into the scholarship behind things like Beowulf. It was a pagan oral tradition recorded by a Christian monk. So, there are examinations of what aspects of that story was in the original pagan tradition and what might have been inserted by the first transcriber to conform to his Christian-based understanding of the world.
In the same way, it’s interesting to note that George Lucas absolutely had no idea that Darth Vader was Luke and Leia’s father or that Luke and Leia were siblings when Star Wars was first created. How does that make that chapter different from the later ones? That is an interesting discussion. Just making up flimsy stuff to try to reconcile them isn’t all that interesting.
I think my opinion here is relevant to this kind of discussion. Are you saying it isn’t?
Yes, entirely. Everyone already knows Star Wars is a work of fiction, and everyone knows that works of fiction often contain mistakes or internal contradictions. Pointing it out in the middle of a conversation like this adds nothing to the discussion, and illuminates nothing interesting about the work.
I mean, if you think I’m wrong, let’s see it. What interesting insights do we get from the observation that, circa 1977, Lucas didn’t intend Luke to be related to Vader, and then, sometime between then and 1980, he decided that they were? If there’s something useful to be mined from that, go ahead and mine it. You don’t need anyone else to do that work for you.
I disagree, and to the extent such speculation looks lame and unsupported to me I’m going to say so.
For pure speculation to cover why Obi-Wan and Yoda put no more work into it, how about this? Uh, it was the Will of The Force, all in capitals just like that: got a feeling, see, and shrugged and went with it; as a Jedi, that’s pretty much my one move: feel it flowing through me, let it control my actions — that’s about all there is to it, plus also sometimes a guy gets a bona fide prophecy.
…so I got that going for me, which is nice.
That’s the excuse every two-timing Jedi tries before getting dumped for cheating.
You will never find a more daunting opponent to argue about what’s appropriate in a thread than a Sith Mod. You must be careful. 
Good… gooooood…