I think, a sub-key would only make sense, as of now, if it's for organisational reasons. Like, if you want to have a job profile without spamming it with personal stuff. However, borrowed trust in this case likely only works, if there is some way for the public to transparently see, how your sub-key is actually connected to your other key.

If you want to actually *hide* personal information, I cannot see how this would work, when you create a new profile based on the private key for your personal profile which contains compromising information. You would need to create a new profile for this to work.

At least these are my thoughts based on my assumptions. I'm far away from being a #Nostr expert, so there is a realistic chance, I might be wrong here.