Thanks for the replies.
I do know and use encrypted disks. But that is more difficult for the average user than a secondary password would be (IMHO, for most users).
Having more lost/forgotten Bitcoins shouldn't be a problem because:
a) Secondary PW would be optional (hence "forgetting" basic users won't use it)
b) It could be the same as the real (just won't display balance without one)
c) REMEMBER your passwords
Hardware wallets:
I don't trust those. What if there is a kill switch implemented in the hardware? What if they go broke and you can't buy a new one? I don't like to depend on something not reproducible on any commodity hardware (or what depends on a server under someone else's control).
Plausible deniability
I agree, this is very hard to implement and will never be perfect. Wouldn't fool any "big players". But it would work for a robber or your wife
I should probably re-think:
Why don't Core asks (can ask) for the one current password right at startup?
I mean the whole wallet should be encrypted including addresses and it simply won't work (or display balances) until the right password given (still: there would be a need for PIN/password to confirm transfers and avoid mistakes, so _I think_ the system how we work with Core cries out for a two level PW system)?