Re: The Dark Knight Returns - if you were to do a sequel/prequel/spin off
^I think you could very well write it in a manner that "Superman had good intentions" with Oliver but it would undermine was Miller's already done. I think the undertones and the insinuation (and the dialogue from Oliver in Dark Knight Returns) implies that this it didn't happen that way. I think it's safe to assume that Superman, being the puppet that he's become, did what he had to do.
It's much like the fight between Superman and Batman at the end issue #4... Superman doesn't really want to fight, and he doesn't even begin to try and hurt Batman until he's pushed. I think the same would've happened with Oliver, and I'd imagine Ollie was antagonizing him... whatever the situation might've been... maybe Superman was there to force Queen into retirement like the others, and Oliver took to kickin Superman's ass. He wasn't going to back down.
Also I think your bit about Jason Todd is also one of those things that's more interesting in that it's not shown. As you said, let your imagination go with it. I think (knowing what came later in the real DCU concerning Todd's fate) it's more fun to just assume that the Joker killed him.