As for calibre, do you mean that can be installed from your plugin list or it will be passed to repo when developed?
In case it can be installed... how?
I mean I am not maintaining it anymore and it will not work with OMV 3.x until somone ports it. So, you cannot install it and it is not in the repo. I will remove it from the list on the omv-extras site so that it does not confuse people.