It's also rumored that Apple is working on a minivan (lol) so I would take such distant rumors with a heavy dose of skepticism.
I do think Apple will produce new case materials next year, though. I'm thinking, a couple bands every 6 months for a while, and a new case material each year, but almost no other changes. Same shape, same features, just maybe some longer battery life. A remote chance of added sensors, but, even that I doubt unless they can work magic to get GPS in there and not drop average battery life at all. Other sensors would be reaching for the remote fringes of society.
It's all about fashion/luxury with this product. Apple has been heavily design oriented for a long time and a continual shift from tech w/ design has been moving towards design w/ tech and this product is the opposite end of that spectrum (beginning being gumdrop iMacs.)
I don't think they will only work on this end of that spectrum, but, I think the place this watch has makes a very different product from which we can expect a very different lifecycle year to year.
SO yeah, platinum watch? Sure. Spring 2016 or Fall 2016. Fall 2015 is too soon for that, but, not for bands. I'd be shocked not to see at least 3 new bands even if it's just colors.