I have a feature proposal regarding autologin:

It is currently not possible to automatically unlock kwallet when using autologin and a non-empty wallet password.
When booting a luks-encrypted system, then systemd prompts for a password. This password is cached in the kernel keyring for user root.
When autologin is enabled, then SDDM should retrieve the password from there and inject it into the pam stack, such that pam_kwallet5.so can use it. With that addition, the following scenario will be possible:

• When booting the machine, I am prompted for the hard disk encryption password
• After entering that password, the system starts up including starting my desktop session and unlocking the wallet (using the same password as provided during boot) without any further interruption
• With the open kwallet, I can also unlock other applications

GDM already has that feature and it doesn't look very complicated.