Jason, I concur with your assessment of the new Atlantis. I had always pined for one, ever since the inception of the model. In fact, other than the "LongLow", it was the first Riv I coveted. But, alas, things have changed (Grant would say for the better).
I finally purchased a Riv, the original 60cm model Sam, in 2009. I now ride a size smaller Sam (the 58cm). I think it is from the 2017 era? At any rate, I had a local builder install canti-bosses, like the original had. I find it to be surprisingly stout. In fact, I regularly load it for bear, and find it to be more bike than I want in some instances (uphill, without a load, for example). I believe that the "new" Sam is more stout than the original. In fact, it felt lighter in the hand to both myself and my mechanic who had history with both of these bikes. Turns out the seat tube had changed from 27.2 to 26.8. My mechanic thinks the thicker steat tube is the answer to the increased heft. That, and the longer chainstays.
All to say, I understand your want for an old school Atlantis in the lineup. But, as someone who rides a larger framed 700c Sam (can't speak to the 650B Sam), it's pretty right on for this purpose. The thing I think that could be improved as a loaded tourer is the tire clearance. Being able to fit a 2" tire under a fender would make it outstanding. I suppose this would make it the de-facto "new Atlantis"? Just musing...
John