Is it only me, or, does it make sense to you, too, to take a convenience (experienced by some subset of PM-receiving users), and swap it for a very probable increase in privacy (experienced by basically every PM-sending user)?
For a start, I don't send nor receive that many PMs, so no PM poweruser opinion here. I agree with you and I'd prefer to just get a notification email with the sole detail that I've a new PM, just that, nothing else. No sender name, no subject, no text body.
If I had really sensitive PMs to exchange, I'd use encryption. I wish it were possible to deploy a GPG public key in user's own profile, which recipients of encrypted PMs could easily fetch for decryption and senders for encryption. So many wishes...