I noticed that I can't add "All current and future organization members" to a board, but rather I can only add current members, and any future members has to be added manually.
Is this feature planned? Can I vote/subscribe to it?
This is not exactly possible, but there's something pretty close that might solve your needs.
Go to "Options" > "Settings" > "Permissions". If you set the visibility to "Organization", you'll be able to enable "Allow organization members to join". Then any person in the organization will be able to add themselves to that board without having to be invited. It won't auto-add them like you asked, but you won't have to invite them manually, and they can easily join boards from the org profile.