I primarily meant the latter, but the former is also possible by two installations of PureOS within the same drive, provided that the boot manager (assuming GRUB) also supports touch screen input.
The realistic solution I am thinking about would be to have two user accounts on the Librem 5: one of them could be a “guest” account; the other one is the administrative/root account. I have yet to read any documentation or mentions of this anywhere.
The idealistic solution is that the unlock screen accepts two passwords and automatically logs in to the associated account depending on the inputted password.