Hiya ! 
I see that the docker image is based on Alpine Linux.
I was wondering if it would be something possible to add cloud-init support on the docker image which would allow us to customize our installation by beeing upgrade proof 
I'd be happy to contribute !
Cheer !
I don't think this will be useful for most Pi-hole users, but you can create your own image using Pi-hole image as base. Start your Dockerfile with:
FROM pihole/pihole:latest AS base
...
My understanding of cloud-init is in initial configuration of virtual machines or lxc containers. I've never seen cloud-init used in the Docker context?
Let's say I want to deploy pi-hole with a management interface and a resolver interface... Cloud-init is pretty simple rather than having to go in the underlaying OS of the docker instance
That's not something that will be considered for Pi-hole. There are far better tools to manage and orchestrate your deployment.