I finally have some really good news on this front. It looks like Apple has fixed this gradual performance degradation bug that happened due to repeated complications update, and that has been there since watchOS3.0.
With watchOS3.2 beta, at least when tested on simulator, I can no longer reproduce this problem. Maybe all my complaining and bug reporting finally worked
As for the next version of the app, it should be a really good one - I've added a true Siri support to the app, so you will be able to to control your thermostats completely hands free, through Siri, without ever needing to start the actual app, or the widget. Next version will only support Siri from the iPhone or iPad, but as soon as wachOS3.2 is officially out, I'll bring the same Siri support to Watch app as well.
That is if Apple approves it first... I've not done things entirely by the book here. You may know that the Siri support for 3rd party apps is very limited in scope, and home devices control is not one of the things they have meant to be officially supported. This, I assume, is the reason that Nest's official app has not made any updates to support this yet (and I'm not aware if any 3rd party apps have attempted to do it either). They way I've made this work is that you're technically speaking 'messages' to your thermostat, but it's very streamlined and easy to perform. I really hope they don't reject it, because I think people will like the way it works.