Qudelix 5k does address these issues:

1. As another commenter mentioned, the battery gets disconnected from the processor when USB power is available. Of course, the battery will still degrade eventually, but it will take a long time and the degradation will neither affect stationary use nor be affected by it.
2. You can configure the timer for the auto turn-off, as well as disable it entirely. Also, the timer only starts when no audio signal is received, so it won't just randomly turn off while you're listening. You can also configure when it's supposed to automatically turn on or off, and this doesn't depend on an audio signal, but whether a USB charger or specifically a device using the 5k as a DAC (depending on what you configure) is detected. So, if you set it up this way, it will turn on as you turn on your device, meaning no delay when the signal comes.
3. Well, okay, true. You can control the volume using your phone or PC without affecting sound quality, though, but that's no replacement for a knob.