The “wake-up” feature could be really interesting. I’m assuming it could be controlled through I2C like the keyboard backlight, etc.? Then it could be exposed to and controlled by PicoMite (and other firmware too).
I’d be happy with the STM32 solution for RTC, especially if it has extra features like this. I’m planning to keep both batteries in my device anyway, and it would be nice to actually use all that battery power for something, rather than just not having to charge it very often. I’m also not concerned about the time accuracy very much either – seems like a good deal to only have to charge it and query an NTP server once a month. 