There won’t be better battery life then this. There will be new features and Hardware, sensors, etc. will became more and more efficient in the time, but the bat. life won’t double. I can swear they will cut the battery in the coming years when they became much more efficient. the same way as they do with iPhones.
All makers offers 1 to 2 days battery life and that is ok, unless they start to put graphene batteries in watches, but this will triple watch price.