Phones have been able to do this for years, but I can't find any modern Linux SBCs with real lower power CPU modes to last for days.
* ideally 1+GHz with 4GB RAM and on-board lipo charging circuit
If something major breaks software-wise you can be pretty sure that the rPi community is large enough to produce a fix within hours.
OTOH if you'd like a new kernel for that fancy $65 big.LITTLE 4GB dualchannel ECC Gigabit PCIe SBC then you're at the mercy of your vendor who considers 4.4 LTS ought to be good enough and already reassigned the entire dev team to work on a future hardware release. ¯\_(ツ)_/¯