Instead of a stand-alone piece of e-waste, how about this: a device with the same format (a ring and an button) but the only thing it does is trigger the pebble watch to start recording a message. This way the microphone isn't needed, just the radio (and much weaker radio at that), and the battery will last exponentially longer. Then just expose the charging terminals so that we can at least hack the device with custom made external charging controllers, or buy a charger separately.
That could be achievable without a battery, using a Piezo button like some Hue remotes... Though not sure with the small form factor.
It's open source and the button is customizable. So it's very likely that could be achieved with the product as-is.
Or better yet. Use your cellphone wich most of us carry 90% of the time?
UX probably not as good in that case. I am thinking about how buggy my voice-remote is for the TV. 1/3 of the time it works, 1/3 of the time there is some lag before it starts working (and requires waiting for feedback i.e. the listening tone before I can speak) and 1/3 of the time it doesn't work at all (never hears me due to lag or booting up or whatever else).
Then just put the button on the watch? In fact, why isn't this just a button on the watch?
Might as well bundle the ring with the watch at that point, and increase the price accordingly, as it's then become an accessory particular to the pebble watch. And including a charging circuit means more complexity and bulk, also leading to an increase in price. And cost is a factor they're optimizing for.