Wow, I didn't know about this!
I have to say, I like the reaper motivation they went with in the end. It's more classically "hard" science fiction, imo. But the other one is interesting, too. Wouldn't have made me think as much though.
I prefer the original motivation, although it still falls prey to the same twisted logic as the Starchild ending, "Reapers want to prevent races from using Mass Effect technology which damages the universe... by wiping out all life and leaving behind the Mass Effect technology for them to find."
Plus it had some set-up in ME2 with the Haestrom sun. The real problem with the Starchild ending was it coming out of nowhere in the last five minutes and completely derailing the plot. When you need the entire Leviathan DLC to provide the only set up and explanation for the ending, you've pretty much failed narrative theory altogether. The set up should always come before the pay-off. It's fine to go back later and provide more context or even shed an alternate light on that pay-off, but you need to establish the premise first to make the audience accept it.
I always felt that Leviathan and From Ashes should have been integral parts of the game and provided us with a ton of set-up and hints at something larger going on with the Reapers that we didn't know, rather than tacked on DLC after the fact. I loved both DLC, but I felt they needed to have been grounded in the main games plot a heck of a lot more than they really were.
I'm considering starting KOTOR, thoughts?
Play it and you'll have the time of your life.
Also avoid about a hundred pages back because I talked about the romance and I got a little spoiler-y, mea culpa.
(Well, it was released over a decade ago, I figured the spoiler warning had expired) 