Somewhat... I more often see the ability to run some fixed-function blocks (RTC, as you mentioned; also ADC running scheduled conversions with a digital compara

Somewhat... I more often see the ability to run some fixed-function blocks (RTC, as you mentioned; also ADC running scheduled conversions with a digital comparator on conversion calling interrupt, as an example) running at this low a clock, with the model being that these low-speed peripherals wake up something else. Having the ability to run a useful set of peripherals /and/ do arbitrary very slow computations to decide about changing clock isn't universal. As an example, even if you had that capability, if you wanted to wake on a complicated condition of an ADC read, you might end up lower total energy use to wake up on the ADC conversion to the RC filter low-MHz speed, do the your computation, and either go back to sleep or continue to wake further, rather than do the computation itself at 32 kHz -- and certainly the former could be lower latency, depending on the complexity of computation.