That depends on the user. I'm assuming you would consider the Droid Incredible released in 2010 obsolete right? My brother just switched from that earlier this month after 4 years of use. It still was running just fine up until a month ago, but most anyone would consider it obsolete.
What I mean is, if a person wants the latest and greatest features, then yes it will be obsolete, as will any mobile device. This notion of future proofing is kinda ridiculous. There is no such thing considering the pace of innovation today. Next year's devices will all most likely come with hardware that will fully support 64 bit. Does that mean that it'll be the last phone you buy for the foreseeable future? No, because these companies need to make sure you come back and give them your business. Apple introduced 64 bit to the iPhone last year, did everyone who bought a 5s skip this year's offering, because they wanted the latest and greatest.
The problem is most all meaningful innovation is done on the hardware side, and so far hardware isn't upgradeable. Now so far as the functions the watch can do today, I would venture that it will still be able to do those years from now as well. With newer functions, assuming the hardware can handle it, those should also be available. But companies like to add features that aren't supported by existing hardware. Why? Because then they can sell you a new device.
So the point is, if the functions that this watch currently performs are all that you need, then it'll most likely function as long as the hardware allows. It may get expanded functionality in the future, but that isn't a certainty. What is certain is that these companies will offer more features and functions in future decices that won't be supported by this device. And that's the case for all smartwatches, smarphones, tablets, TVs, computers, cars, etc, etc. If you're happy with what it does today, it'll be okay for quite awhile. But if you're going to always want the latest and greatest features, then it'll be obsolete the second the next version is available.