[U-Boot] Where is the edge between a loader and (microkernel) OS?

Good Day

I'm looking at u-boot source code, and see a huge amount of hardware drivers, used only for the loader. On the other side, modern Linux kernels eat a more than half of RAM on cheap embedded modules like HLK-R04.

Is it suitable to morph u-boot into tiny embedded microkernel OS adding multitasking scheduler or share its drivers for i/o with some other tiny RTOS?

------------------------------ With best regards, Dmitry Ponyatov, CNC/embedded engineer, tel. +7 917 10 10 818