The absolute prefix requirements (similar to Nix, and I guess for the same reason) mean this probably can't be used where it would be most useful - on machines that you don't control.

I wonder if anyone will ever make something like this but where all the software has to be relocatable (no hard-coded absolute paths).

I guess a lot of software would be excluded or need patching, but I think it would be useful and maybe it would encourage Linux developers to stop bloody hard-coding absolute paths like it's still the 90s!