IMO, that's just inviting disaster. The client should only be running on machines that are inherently secure. Doing this will encourage people to run the client on insecure machines, which will compromise their wallets even if they are encrypted. Strong passwords will be forgotten, leading to lost BitCoins. Weak passwords will be brute forced, accomplishing nothing.
Yeah, but a forgotten password is everybody's own fault, while the average BTC user can't be expected to only keep his wallet on his walled-off linux machine with only carrier pigeon connectivity.
Of course, most known cases of theft have been linked to gross negligence, but that's just how people work - you don't worry until it's too late.
I, for one, would welcome wallet encryption, even if it's not 100% secure and perfect. I mean, what is 100% secure?
But a forgotten password results in lost coins for the whole network, while stolen coins are still circulating.