For who may interest this subject. I've published a rough version of a ruby gem called capistrano-froxlor. It adds Froxlor cli functions to Capistrano 3. This gem does not deploy Froxlor itself. It can be useful if you like to deploy applications to a froxlor machine. We use it for deploying TYPO3 sites, but of it could be used for any application that van run inside a Froxlor domain.
For now it can create or update subdomains and can create databases for a customer. Perhaps more functionality will follow. I'm open for feature- or merge requests.