there are projects to multiboot for uboot but is this really a need ?
all games & others things could run with all different possible OS,
belong the work to port a multiboot solution it will also take the boot time longer, and will need a bit of work to make the different OS compatible too (patch auto mount partition id etc …)
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launch a different menu interface is as easy as edit the .xinitrc file (if xserver used), sure in the long run things could be automated
also launchers are dedicated to the system, there is tiny difference who could breaks things, major one’s are package system and the wifi management lib
in arch netctl is used, fantasti can create config for it but cannot config others for now, same thing for clockwork launcher who cannot config netctl
fantasti also manage pacman to directly install 3rd packages, and for now cannot install from apt, apt code is included (from pingu apt manager) but need some work to use it properly.
also for this way we need clean packages for launchers, clockwork one have some deps so it need more work
for fantasti it’s pretty easy to package as it’s binary and for retroarch it must be ok as all OS use it.