I want to kindly ask you if you consider the Ubuntu Linux distributions among the fully supported operating systems for Foreman - Katello as managed systems.
Also, I would like to know if you have plans for long-term supporting Ubuntu Linux distributions.
If you are asking whether you can install Foreman & Katello on Debian - this is not a supported scenario.
You can manage Debian content with Katello, where Foreman/Katello are installed on a RH-based OS like Centos.
Since we are a FOSS community, if you or a group of people would be interested in further development of Katello for Debian installations, the community would be happy to answer any questions and support you in the effort. I haven’t heard of anyone actively working on this for now though.