For example, this question might be a great example of someone wanted to break into a system but masking the question as a "problem". In this case, assuming I can provide an answer, should I refrain to do so?
I would answer the question.
For one: we assume that having physical access to a system means a user can do anything to that system. He clearly states he knows how to do this from GRUB (what would be the answer on how to change it and that would have been a dupe though).
And the answer to his question is safe too: it is NO. It is in no way possible to get a plain-text version shown of a password. Even when root those are not shown.
So any way you look at it the question in itself warns no special prudence. Though it is not about Ubuntu (as the close reason given) but about security.