Might not have to wait for the next generation of hardware since the current generations all supported both Wi-fi and Bluetooth.
I just mean that it'll be announced with the next Apple Watch, like HomeKit was announced at an iPhone event but works with older devices. Every year, there's a major new feature to focus on. I think that health measuring add-ons will be the next one for Apple Watch.
An aside, I think that the next Apple Watch will have a smart connector in the strap link. A glucose monitor could be a bracelet that docks into the Watch's smart connector. Those accessories will of course only work with the new Apple Watch. Wireless accessories like a sleep monitor would work with older devices.