I’ve done some study before I post. According to this post, standby mode doesn’t stop the radio. The reason for that is it takes 30s to 1min to reconnect. I would assume the wifi is up as well.
Actually I am fine with a manually triggered standby mode that stop radio and all wifi (upstream/downstream), or only allow upstream wifi if it is already connected. What I want to achieve is that the device can easily survive a day (12-15 hours) without charging.
Also, I have checked the list of current feature request 2023 and found nothing remotely relevant to this.