Ok, from what I understand, the main process is to load the ROM file in RAM, and patch it so it can run from RAM. With some efforts the EmuTOS build process could probably produce those files.
On the other hand, on Atari machines EmuTOS is also provided in a RAM variant (named EmuTOS-RAM or EmuTOS-floppy). That one is designed to be run from RAM, at a fixed address. The same method could be applied on Amiga.
To do that, I just need an AmigaOS bootstrap program which allocates some RAM and loads a data file into it. Ideally, that should be a simple bootblock routine which loads the data from sectors using trackdisk.device or similar.
If someone can provide me such bootblock program in assembly language, then chances are good that we will have an EmuTOS-floppy some day. In other words, that would mean loading EmuTOS from a boot floppy, just like a game. But that eats the RAM.