I'd love to see improvements to the password generator feature. It's very handy, but unfortunately it doesn't allow customization. Different sites have different requirements; some (bizarrely) don't allow special characters, or have a cap on the length. Sometimes the generated password doesn't work. 1Password (as well as the generator in the Keychain Access app) allow you to customize the formula (how many numbers, how many digits, length, etc). I'd like to see that feature built in to Safari.