a) goes against security goals of Secure Boot enabled Ubuntu. And it still doesn’t solve anything, see that thread for details on why encrypting /boot does not increase security. First, its contents are pretty much public knowledge and, second, an attacker could just put a key grabber on the ESP and have grub run that first.
b) proposes to hand out footguns to all the novice users, who won’t know what they’re in for.
c) defeats lockdown
BTW, b) is already there; just disable Secure Boot.