Heyo,
We are currently working on releasing Hero Siege for PS4. We are in the midst of QA and fixing sony's bug/requirement list as we go.
Hero Siege will be crossplatform on PS4 with PC / Mobile (HOPEFULLY). There are ton of restrictions and guidelines we need to work on for this to happen so it will take some time unfortunately....
Switch will be cross with PC / Mobile as well, but not with PS4 due to Sony's policies. I know this is tricky but we will try to make it as good as possible.